Your reward is based on your hash rate, not the pool size.
The only difference on your reward between pools is the fees and variance
(as long as the pool gets some blocks every diff change/every 2 weeks)
I'm sorry, this is very likely to be a 'terminology issue' on my part.
If you have 100 users, and you hit a block, isn't the reward divided by the 100 users, and
the ratio is of on the hash rate/hashing done by each and therefore if you are in a pool,
with 1000 users, your reward would be LESS?