First of all, as I said Luke was not fried directly to the face. Palpatine's lightning hit nothing BUT his face.
Secondly, the GRAND TOTAL time itself does not matter. What matters insofar as what I am speaking about is the longest individual segment of uninteruppted exposure, which Palpatine would have easily been subjected to.
Assume it is twice as long for Luke... it would look something like this:
Luke:
____8____ __7______ ___8______ _____10_______ ____8____
Palpatine:
_____________25____________