Quote from Dan10105
I would just double the size and put down half slabs, although I had no idea that it killed the spawning rates by that much. Correct me if I'm wrong, but shouldn't your pads go from 9 blocks to 8 blocks, thus reducing spawning spaces by 11% and not 50%?
Not everyone uses 3x3 spawning pads (though they are the best or close to it if you are just relying on the mob walking off the ledge).
OP: You don't have enough spawning space as is. I would add a layer above that one and then add the half slabs (though why you think it will cut your spawning rate in half is beyond me).