I have been researching pool centralization and manipulation, one of the things I found is that discus fish and ghash set their accepted block size very low. Discus fish obscenely low.
This allows them to plow through more of the smaller blocks faster than pools that play fair.
There's no such thing. "Smaller blocks" (presumably by that you mean ones with less transactions) take just as long on average to solve as larger ones.
The time needed to find the block should be the same, in statistical sense.
But the time needed to propagate a smaller block to the network should be slightly shorter, giving the miner a slightly advantage in orphan block race.