So! I've made a giant mob spawner/killer up in the sky (y=220-235) over an ocean. Light level 1 spawn floors, 540 block area, 3 high, periodic water flush that pushes mobs into a pit, where fall damage kills them.
Problem is, mobs seems to rarely spawn inside, and endermen just vanish. I know they teleport on contact with water, but shouldn't they appear outside the trap on one of the catwalks? The floor they land on is ~40 blocks lower, and there's nothing else up that high.
So my question(s) are, why aren't more monsters spawning? I'll leave it running for half an hour, and there will be 2 spawns. Other times, I'll get 30 kills in 10 minutes. Any idea why?
Bonus round: Where the hell are the endermen going? Why do they hate my trap?