My bad on the 10% miners, the double coins was on solo mining not pool mining.
Thanks, I'm more comfortable with what you are representing.
I can see now that the variance for each pool size is caused more by the difficulty changes than anything else. If the difficulty remained static, results would be much more uniform over a long period of time. At least that is what I would expect.
Yes, as the difficulty changes reduce to 0 (on average - they can't actually hit 0 and just stay there) then the advantages for larger mining pools would be eliminated in the longer-term. The problem, of course, is that it's unlikely we'll see a 0% average difficulty any time soon.