I think if TA no prep completion time to total time ratio is above 2.5 it's not the time pressure based exams I'm referring to.

I didn't get those exams in math courses. Engineering courses I did get those where some of the point of the test is the speed of your pattern matching ability (did you use design skills to reason about it or did you brute force a solution).

Math you're already extrapolating theory and you need ample time for that.