Kevin,
According to the chart I have (mo pinel's chart--it also matches the chart used by Bill Taylor) it would really depend on the flex they have in their thumb.
Example of how to figure this out is this---hold your hand where you are looking at the back of the hand with all 4 fingers straight and together with the fingers pointed to the left (for righties), and the thumb at a 90 degree angle (or as much as it bends). You want to apply a little pressure to see how much the thumb can flex back to the right. Use this method when checking for forward or reverse pitch---
He has it listed in terms of degrees.
Very flexible when applying the slight pressure to the thumb---if it bends back
-150 degrees that is very flexible the pitch for the 4 1/8 would be 1/8 forward for the 5 inch span 5/16 reverse
-135 degrees is average 4 1/8 would be 1/16 forward and the 5 would be 3/8 reverse
-105 degrees is some flex 4 1/8 would be 0 and the 5 would be 7/16 reverse
-90 degrees would be average tight
4 1/8 would be 1/16 reverse and 5 would be 1/2 reverse
-75degrees would be very tight and the 4 1/8 would be 1/8 reverse and the 5 would be 9/16 reverse.
I hope you can understand the angles part of it, and the method I tried to explain.
When you say under palm, I am a little confused. Do you mean forward and reverse pitches or are you speaking in terms of the lateral pitch of the thumb?