slimes won't spawn if there is a block above them

so i made a under ground slime farm in a slime chunk, i check the slime chunk app slime finder to check the start and end to the chunk and its right but nothing will spawn. so i loaded my world in creative to see what was going on and once i cleared all the blocks above the chunk it started spawning. so i thought they needed sun light. but once i put more levels on top they weren't spawning anywhere but the top level even with sun light and 4 block gape between them