I'm trying to make a biome where Blazes can spawn naturally above any lava blocks. I made a new monster that extends the EntityBlaze class, and made this its spawn check:

 

public boolean getCanSpawnHere() {
boolean boundCheck = this.worldObj.checkNoEntityCollision(this.boundingBox) && this.worldObj.getCollidingBoundingBoxes(this, this.boundingBox).isEmpty();
int i = MathHelper.floor_double(this.posX);
        int j = MathHelper.floor_double(this.boundingBox.minY);
        int k = MathHelper.floor_double(this.posZ);
return boundCheck && this.worldObj.getBlock(i, j - 1, k) == Blocks.lava;
}

 

and then added it to the biome spawn list with:

this.spawnableMonsterList.add(new SpawnListEntry(ESIVBlaze.EntityESIVBlaze.class, 100, 2, 4));

 

However, the blazes never spawn in the biome.

I've narrowed down the issue, it seems whatever controls the natural spawn of monsters does not take fluid blocks into consideration. If I set the spawn check to detect lava 2+ blocks beneath it, then the blazes will spawn, but only if there is a solid platform above the lava pool. Likewise, if I set the spawn check to detect lava in a radius around the blaze instead of directly beneath, then they will only spawn on the coastline around the lava pool, not on the lava itself.

 

Does anyone know where the code is located that controls natural spawn, and/or if there's a way to modify that behavior?