Help prevent mob from spawning underground.

Im making a new mob that spawns in a biome, however whatever i do i cant prevent it from spawning underground. Here are the details of the mob.

It's a mob type because it attacks (not sure if this affects anything)

The spawning is ambient

There is a procedure that checks if there is cave air, and if there is, it will not spawn but it doesnt work

if not get block at xyz = cave air return true else return false

Please give any ideas, thank you.