For the sake of science, I have refined my calculation.
Assuming a mean base hit chance of 70% and a standard deviation of 2 (which I think is pretty reasonable) yields a result of 4.1
Wolfram"Code": sum from n=1 to 19 (erf((n - 6 - 0.5)/2 , (n - 6 + 0.5)/2)(1 - (n/20)^2 - (20-n)/20)) /erf((1 - 6 - 0.5)/2 , (19 - 6 + 0.5)/2) *100 /5
If anyone feels like playing around with it:
To change the mean hit% --> replace the four 6s
To change standard deviation --> replace the four 2s
Couldn't find a way to declare constants
