Your theory on small sets with corresponding big sets was, of course, correct. The number wound up at 3.4 to 1 though on those 10 small sets v. 10 large corresponding sets. You can see below.
The individual sets are interesting though.....there are 8x more N2's graded than N36's which I figured would be lower. On the other hand, there are more N44 World's Decoration large format graded than N30 small format for a ratio of 0.7 to 1; the only one with a sub-1 ratio.
I also did a ranking by total PSA population by issue, so you can see the most popular issues or most graded issues (in all grades total). No surprise but N28 is far and away the winner in that race with N2 a distant second. And then only three other issues with more than 1000 graded for N11, N20 and N29.
Kind of surprised N9 flags aren't a little higher than they were with so many back variants and the Fancy cards and other issues. Also interesting that N11 States were so high and N20 chickens. Guess there are a lot of chicken collectors out there.