Couple of minor points

1. As a nit, I think you should exclude foreign players from the calculation (Vadeeva and Gulich) and slide up the American and Canadian-born players so that you're comparing apples to apples (North American players as ranked in HS and as selected in the WNBA draft among US/Canadian players).

2. Without looking at the raw rankings, it seemed that the top 6 ranked HS players performed up to expectation. (your 3 or 4 sigma cases that were clearly better. The next set of players were closer together and more difficult to separate). It would be interesting to see if this occurred regularly.

3. It might be interesting to look at ranked players who didn't live up to expectations and speculate why that happened (too high an initial ranking, twiners who were affected by college game, failure to develop, etc.)