Bruce and Dan are probly right.
Try to verify if the spine is too stiff.Borrowa buddy's longer shaft and/or throw a 125 grain tip on the arrow to see if you can weaken the dynamic spine. If the arrows are good in the 70, they're probly not right for the 60. You could turn the 70 down to 60 to see if the arrowsare too stiff for 60.

This would be a lot simpler than switching risers although I admire your willingness to diassemble stuff.