are doing better against expectations than the hypothetical MAAC is because you use cumulative stats.

Consider, for example, a hypothetical where a conference gets four teams into the tournament, all of which are 2-seeds. If all four of those 2-seeds made the Sweet 16, your system would give that conference a score of 1.44. In contrast, it would give a conference that gets it's lone 16-seed into the Sweet 16 a score of 1.

I don't think anyone could truly say that a conference that gets four 2-seeds into the Sweet 16 outperforms expectations more than a conference that got its lone 16-seed into the Sweet 16. But, your method would say that the former outperforms the latter by a fairly wide margin.