Have you tried walk-back tuning? My BH's and FT's were about 3 inches apart. The BH's grouped well together as did the FT's. After walk-back tuning and adjusting the L-R on my rest, they now group right together.
http://www.archerytalk.com/vb/showthread.php?t=454036

Any Minor rest misadjustment will start to show up at about 20+yards and get worse as you move back. Walk back tuning helps correct the rest position. Best "fine tune-up" I've ever tried.