Possible reasons: orphaned blocks, hardware errors, shitty pool (by far the worst: ghash.io)
Also your Antminer won't run at 100% hashing power all the time. Have you tried eligius.st yet?
If you don't mind me asking, why would you say ghash.io is the worst? OP says he's got roughly 1.14th/s and is only getting .09 per day with his pool and I have about 760 gh/s on ghash.io and i'm getting about the same per day.