Hey guys thanks for the responses.
n3m3c1s, where did you get that information about the calculations? Is that in the game somewhere?
The only talent that I have on Madora that might be influencing this is "What A Rush", but that should only be triggering at <30%. Perhaps this is a bug?
Going by n3m3c1s formulas, Constitution shouldn't affect Turn Action Points at all, but it clearly is from my screenshots :S.