Nether biomes don't generate groundcover over Y=127 even if there is terrain.

Increasing the height of the Nether using custom JSON world generator files does not increase the height at which groundcover such as soulsand or basalt or nylium generate.

World generator json.

{
"bonus_chest": false,
"dimensions": {
"minecraft:overworld": {
"generator": {
"biome_source": {
"seed": 1,
"large_biomes": false,
"type": "minecraft:vanilla_layered"
},
"seed": 1,
"settings": {
"bedrock_roof_position": -10,
"bedrock_floor_position": 0,
"sea_level": 4,
"disable_mob_generation": false,
"default_block": {
"Name": "minecraft:stone",
"Properties": {}
},
"default_fluid": {
"Name": "minecraft:lava",
"Properties": {
"level": "0"
}
},
"noise": {
"top_slide": {
"target": -35,
"size": 32,
"offset": 0
},
"bottom_slide": {
"target": -3,
"size": 6,
"offset": 1
},
"sampling": {
"xz_scale": 1,
"xz_factor": 150,
"y_scale": 1,
"y_factor": 50
},
"size_vertical": 2,
"size_horizontal": 1,
"height": 256,
"density_factor": 0.1,
"density_offset": -0.05,
"random_density_offset": true,
"simplex_surface_noise": true,
"island_noise_override": false,
"amplified": false
},
"structures": {
"stronghold": {
"distance": 32,
"count": 128,
"spread": 3
},
"structures": {
"minecraft:village": {
"spacing": 32,
"separation": 8,
"salt": 10387312
},
"minecraft:desert_pyramid": {
"spacing": 32,
"separation": 8,
"salt": 14357617
},
"minecraft:igloo": {
"spacing": 32,
"separation": 8,
"salt": 14357618
},
"minecraft:jungle_pyramid": {
"spacing": 32,
"separation": 8,
"salt": 14357619
},
"minecraft:swamp_hut": {
"spacing": 32,
"separation": 8,
"salt": 14357620
},
"minecraft:pillager_outpost": {
"spacing": 32,
"separation": 8,
"salt": 165745296
},
"minecraft:stronghold": {
"spacing": 1,
"separation": 0,
"salt": 0
},
"minecraft:monument": {
"spacing": 32,
"separation": 5,
"salt": 10387313
},
"minecraft:endcity": {
"spacing": 20,
"separation": 11,
"salt": 10387313
},
"minecraft:mansion": {
"spacing": 80,
"separation": 20,
"salt": 10387319
},
"minecraft:buried_treasure": {
"spacing": 1,
"separation": 0,
"salt": 0
},
"minecraft:mineshaft": {
"spacing": 1,
"separation": 0,
"salt": 0
},
"minecraft:ruined_portal": {
"spacing": 40,
"separation": 15,
"salt": 34222645
},
"minecraft:shipwreck": {
"spacing": 24,
"separation": 4,
"salt": 165745295
},
"minecraft:ocean_ruin": {
"spacing": 20,
"separation": 8,
"salt": 14357621
},
"minecraft:bastion_remnant": {
"spacing": 27,
"separation": 4,
"salt": 30084232
},
"minecraft:fortress": {
"spacing": 27,
"separation": 4,
"salt": 30084232
},
"minecraft:nether_fossil": {
"spacing": 2,
"separation": 1,
"salt": 14357921
}
}
}
},
"type": "minecraft:noise"
},
"type": {
"name": "minecraft:overworld",
"ultrawarm": false,
"natural": true,
"shrunk": false,
"piglin_safe": false,
"respawn_anchor_works": false,
"bed_works": true,
"has_raids": true,
"has_skylight": true,
"has_ceiling": false,
"ambient_light": 0.0,
"logical_height": 256,
"infiniburn": "minecraft:infiniburn_overworld"
}
},
"minecraft:the_nether": {
"generator": {
"biome_source": {
"seed": 1,
"type": "minecraft:multi_noise",
"biomes": [
{
"biome": "minecraft:basalt_deltas",
"parameters": {
"temperature": -0.5,
"humidity": 0,
"altitude": 0,
"weirdness": 0,
"offset": 0.175
}
},
{
"biome": "minecraft:crimson_forest",
"parameters": {
"temperature": 0.4,
"humidity": 0,
"altitude": 0,
"weirdness": 0,
"offset": 0
}
},
{
"biome": "minecraft:nether_wastes",
"parameters": {
"temperature": 0,
"humidity": 0,
"altitude": 0,
"weirdness": 0,
"offset": 0
}
},
{
"biome": "minecraft:soul_sand_valley",
"parameters": {
"temperature": 0,
"humidity": -0.5,
"altitude": 0,
"weirdness": 0,
"offset": 0
}
},
{
"biome": "minecraft:warped_forest",
"parameters": {
"temperature": 0,
"humidity": 0.5,
"altitude": 0,
"weirdness": 0,
"offset": 0.375
}
}
]
},
"seed": 1,
"settings": {
"bedrock_roof_position": -10,
"bedrock_floor_position": -10,
"sea_level": 0,
"disable_mob_generation": false,
"default_block": {
"Name": "minecraft:netherrack",
"Properties": {}
},
"default_fluid": {
"Name": "minecraft:lava",
"Properties": {
"level": "0"
}
},
"noise": {
"top_slide": {
"target": -150,
"size": 20,
"offset": 0
},
"bottom_slide": {
"target": -10,
"size": 8,
"offset": -1
},
"sampling": {
"xz_scale": 1,
"xz_factor": 80,
"y_scale": 3,
"y_factor": 60
},
"size_vertical": 2,
"size_horizontal": 1,
"height": 256,
"density_factor": 0,
"density_offset": 0.02,
"random_density_offset": true,
"simplex_surface_noise": false,
"island_noise_override": false,
"amplified": false
},
"structures": {
"structures": {
"minecraft:village": {
"spacing": 32,
"separation": 8,
"salt": 10387312
},
"minecraft:desert_pyramid": {
"spacing": 32,
"separation": 8,
"salt": 14357617
},
"minecraft:igloo": {
"spacing": 32,
"separation": 8,
"salt": 14357618
},
"minecraft:jungle_pyramid": {
"spacing": 32,
"separation": 8,
"salt": 14357619
},
"minecraft:swamp_hut": {
"spacing": 32,
"separation": 8,
"salt": 14357620
},
"minecraft:pillager_outpost": {
"spacing": 32,
"separation": 8,
"salt": 165745296
},
"minecraft:stronghold": {
"spacing": 1,
"separation": 0,
"salt": 0
},
"minecraft:monument": {
"spacing": 32,
"separation": 5,
"salt": 10387313
},
"minecraft:endcity": {
"spacing": 20,
"separation": 11,
"salt": 10387313
},
"minecraft:mansion": {
"spacing": 80,
"separation": 20,
"salt": 10387319
},
"minecraft:buried_treasure": {
"spacing": 1,
"separation": 0,
"salt": 0
},
"minecraft:mineshaft": {
"spacing": 1,
"separation": 0,
"salt": 0
},
"minecraft:ruined_portal": {
"spacing": 25,
"separation": 10,
"salt": 34222645
},
"minecraft:shipwreck": {
"spacing": 24,
"separation": 4,
"salt": 165745295
},
"minecraft:ocean_ruin": {
"spacing": 20,
"separation": 8,
"salt": 14357621
},
"minecraft:bastion_remnant": {
"spacing": 27,
"separation": 4,
"salt": 30084232
},
"minecraft:fortress": {
"spacing": 27,
"separation": 4,
"salt": 30084232
},
"minecraft:nether_fossil": {
"spacing": 2,
"separation": 1,
"salt": 14357921
}
}
}
},
"type": "minecraft:noise"
},
"type": {
"name": "minecraft:the_nether",
"ultrawarm": true,
"natural": false,
"shrunk": true,
"piglin_safe": true,
"respawn_anchor_works": true,
"bed_works": false,
"has_raids": false,
"has_skylight": false,
"has_ceiling": false,
"fixed_time": 18000,
"ambient_light": 0.1,
"logical_height": 256,
"infiniburn": "minecraft:infiniburn_overworld"
}
},
"minecraft:the_end": {
"generator": {
"biome_source": {
"seed": 1,
"type": "minecraft:the_end"
},
"seed": 1,
"settings": {
"bedrock_roof_position": -10,
"bedrock_floor_position": -10,
"sea_level": 0,
"disable_mob_generation": true,
"default_block": {
"Name": "minecraft:end_stone",
"Properties": {}
},
"default_fluid": {
"Name": "minecraft:air",
"Properties": {
"level": "0"
}
},
"noise": {
"top_slide": {
"target": -3000,
"size": 64,
"offset": -46
},
"bottom_slide": {
"target": -30,
"size": 7,
"offset": 1
},
"sampling": {
"xz_scale": 2,
"xz_factor": 80,
"y_scale": 1,
"y_factor": 160
},
"size_vertical": 1,
"size_horizontal": 2,
"height": 128,
"density_factor": 0,
"density_offset": 0,
"random_density_offset": false,
"simplex_surface_noise": true,
"island_noise_override": true,
"amplified": false
},
"structures": {
"structures": {
"minecraft:village": {
"spacing": 32,
"separation": 8,
"salt": 10387312
},
"minecraft:desert_pyramid": {
"spacing": 32,
"separation": 8,
"salt": 14357617
},
"minecraft:igloo": {
"spacing": 32,
"separation": 8,
"salt": 14357618
},
"minecraft:jungle_pyramid": {
"spacing": 32,
"separation": 8,
"salt": 14357619
},
"minecraft:swamp_hut": {
"spacing": 32,
"separation": 8,
"salt": 14357620
},
"minecraft:pillager_outpost": {
"spacing": 32,
"separation": 8,
"salt": 165745296
},
"minecraft:stronghold": {
"spacing": 1,
"separation": 0,
"salt": 0
},
"minecraft:monument": {
"spacing": 32,
"separation": 5,
"salt": 10387313
},
"minecraft:endcity": {
"spacing": 20,
"separation": 11,
"salt": 10387313
},
"minecraft:mansion": {
"spacing": 80,
"separation": 20,
"salt": 10387319
},
"minecraft:buried_treasure": {
"spacing": 1,
"separation": 0,
"salt": 0
},
"minecraft:mineshaft": {
"spacing": 1,
"separation": 0,
"salt": 0
},
"minecraft:ruined_portal": {
"spacing": 40,
"separation": 15,
"salt": 34222645
},
"minecraft:shipwreck": {
"spacing": 24,
"separation": 4,
"salt": 165745295
},
"minecraft:ocean_ruin": {
"spacing": 20,
"separation": 8,
"salt": 14357621
},
"minecraft:bastion_remnant": {
"spacing": 27,
"separation": 4,
"salt": 30084232
},
"minecraft:fortress": {
"spacing": 27,
"separation": 4,
"salt": 30084232
},
"minecraft:nether_fossil": {
"spacing": 2,
"separation": 1,
"salt": 14357921
}
}
}
},
"type": "minecraft:noise"
},
"type": "minecraft:the_end"
}
},
"seed": 1,
"generate_features": true
}