I tracked volleyball/football/boys basketball/girls basketball for fifteen years back and then compared success to different factors looking for things that could be used to predict success. Enrollment ration compared to the largest school in class was not a predictive factor. The only highly predictive factors were:
1) low poverty rate as measured by free/reduced lunch numbers
2) past success
3) proximity to a large school (I think I used 15-mile radius and schools of 600+ as large)
(I should list "being a private school" but I had tossed that out as a possible solution in Nebraska beforehand because of politics. Plus, I believe that the advantages of private schools are more explainable through the above factors because they all predict success by public schools. So, I decided I wasn't interested in studying school funding effects.)
I did try other factors. I remember looking at the valuation of each district per pupil, but that yielded no predictive effect at all.
Here's the presentation I put together with my numbers:
Factors that predict athletic success
I did an episode of my podcast running thru the numbers last fall when the re-classification proposal was being considered by the NSAA members. It is
episode 10 here.