Any R-D longbow of good design should handle 31”s. I set the grip forward a bit on mine to help a little with my draw. My 62” doesn’t even feel bad at 31. As long as you have a consistent poundage gain at the end of the draw cycle it’ll feel fine. When it starts to jump its noticeable on the scale, at least from what I’ve built. If a bow has a flat draw force curve it’ll feel nice on the draw but it’ll be slow and most likely have hand shock. If you can build a bow with a good amount of preload and gain a lot of poundage at the beginning of the draw cycle then level off at the end of the draw to 2 or 2.5 pounds per inch your gonna have a good preforming bow. I haven’t got my one piece longbows to my liking yet but the one I built for the bow swap was better. The takedown I just built seems to preform very well. They are both 64” drawn to 31