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 1.18.1.

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.