first of all... I dont think you are anywhere near underspined. I have shot those arrows much longer with much higher draw weight with no tuning problems...
Second... why in the world would you paper tune at 10 yards? Move up to 5 feet, paper tune, move back, broadhead tune... you should be good to go. All you learn when paper tuning at 10 yards is the obvious... fletching works. You need to know what the arrow is doing when leaving the bow, not once the blazers have done their job. You will certainly learn even less be shooting through paper further back.
Honestly I have seen very few accuracy issues with field points with an underspined arrow, the problems comes when trying to shoot a broadhead. I know of nothing that will cause an arrow to be accurate at 20 and 40 and not at 30 (physics). I think that is mostly mental. the amount of "oscillation" in an arrow is very little, most likely not something you would notice from a bow that is slightly out of tune... many times different colored fletching combos will cause an arrow to look like it has different flight.
Joe
