My FC400 did the exact same thing. I screwed with it for months trying to get it closer to what should be right. Tuned in as a good 1 inch nock high. Everytime I tried something, it wanted to be VERY nock high. Tore it completely down and re-installed everything. It wanted to be set back to the same screwed up position. Finally, deer season got close enough, I just ended up leaving it alone. Now that deer season is over, I have all year to try to get it right.
2006 Rytera Bullet X 60#---2008 Moab 70#
2008/12 Firecat 60#--- 2010 Warthog 70#
2010/2012 Alien X 65# 2011 Onzas 60 & 70#
2009 Warthog 70#---2009 Firehawk 70#
2010 Strother SR-71 65# & 2012 Strother Rush 65#
I hunt, therefore I eat. lol