Potion particles spread always from the center of a block, regardless of impact

This can cause potion particles to sink into the ground when thrown onto farmland, grass paths, bottom slabs, and other blocks without a solid top face.

affects 20w27a

Can confirm in 20w46a.

Can confirm in 21w05b.

Can confirm in 21w06a.

Can confirm in 1.16.5 and 21w08b. Video attached.

Can confirm in 21w15a.

Can confirm in 21w16a.

Can confirm in 1.17.

Can confirm in 1.17.1.

Can confirm in 1.18.1.

Can confirm in 1.18.2.

Code analysis (Mojang mappings, 22w15a): ThrownPotion#onHit() creates a level event when the potion hits something, using the block position instead of the entity position (LevelAccessor#levelEvent(...) requires a BlockPos):

...
int $$5 = $$2.hasInstantEffects() ? 2007 : 2002;
this.level.levelEvent($$5, this.blockPosition(), PotionUtils.getColor($$1));
...

In LevelRenderer#levelEvent(...):

...
                Vec3 $$25 = Vec3.atBottomCenterOf($$2);
                ...
                SimpleParticleType $$30 = $$1 == 2007 ? ParticleTypes.INSTANT_EFFECT : ParticleTypes.EFFECT;
                for (int $$31 = 0; $$31 < 100; ++$$31) {
                    double $$32 = $$4.nextDouble() * 4.0;
                    double $$33 = $$4.nextDouble() * Math.PI * 2.0;
                    double $$34 = Math.cos($$33) * $$32;
                    double $$35 = 0.01 + $$4.nextDouble() * 0.5;
                    double $$36 = Math.sin($$33) * $$32;
                    Particle $$37 = this.addParticleInternal($$30, $$30.getType().getOverrideLimiter(), $$25.x + $$34 * 0.1, $$25.y + 0.3, $$25.z + $$36 * 0.1, $$34, $$35, $$36);
                    ...
                }
...

This uses Vec3.atBottomCenterOf(BlockPos) as the "reference" position to spawn the particles, which is (x + 0.5, y, z + 0.5), so the particles are spawned around the bottom center of the block.

Confirm in 1.19.1-pre2

Can confirm in 1.19.