Cutting an arrow too short from my experience has been one of the things that limited the set up from being as forgiving as possible. For many years I would cut arrows too short and not shoot as well. It is not that a shorter arrow is going to shoot terrible, but if you are looking for the "best" or optimum forgiving set up, then shorter arrow, IMO is just not as forgiving.
I take an arrow and do a check to see where it has the least amount of vibration. Where that point is behind the arrow point is where I want the last point of contact with the shelf or end of the arrow rest. This is usually from 2.5 to 3 inches behind the back of the point.
To check you take an arrow and rest it on the edge of a table. Take your left hand and hold the nock. Take your right hand and pull down to make the arrow bounce. Where the least vibration is, is the point you want touching your rest. Really need a youtube video of this!