If your engine is out, gliding with the prop at the cruise setting would keep engine rpm up, the prop is windmilling, keeping the hydraulics and electrics going. But there is much straight drag from the prop, and pulling back to coarse will give less straight drag and a reduced rate of descent. What happens, though, is that the windmilling effect lessens and the prop slows down. So, if you need every last yard to reach your chosen field pull the prop lever right back.
If this is a practice forced landing DO NOT FORGET to run the lever forward for the overshoot!