The EVO is hard on arrows. If the chart says your on the edge of spine you are probably under spined shooting the PSE. Although I would venture to say your 31" of arrow and 100 grain broadhead puts you very light on the front. So I'd expect your FOC is out of whack. Also, where did you get the arrows? What vanes? Do they have a twist/helical?
Judging an arrows flight by the angle of the arrow in the target is not always a true test either. You have to watch them in flight to be sure. Especially if your target has multiple layers that the heads enter at an angle. Montecs out of the box are not the sharpest tool. So the dull surfaces will easily follow the path of the media orientation. If they are at different angles to one another it's a good bet this or poor FOC in wind is what's happening.
Good luck! Sure hope you're having some fun
