Flopping set

[Sinnerman]

I have a question about the chance that you will flop a set.
The chance is 1 in 8 times avg. 13%.
But when I look at my pokertracker stats, I notice that the higher my pair is, the more profit I make with it. I know this probably has also to do with overpair value, but I was wondering;
Do middle pair holdings flop a set more regulary because people often fold low cards, and play their high cards.

So I figure high pairs hit sets less frequently cause of the higher chance people holding the same picture. And a low pair hits also less because most people fold those.
So middle pair hits more?

Does this make sense? Thx