the answer to your question is fairly simple, though. if it's not the intonation screw fretting your string off, then it's fairly obvious that it's the 7.25" radius fretboard that is fretting your string off.
imagine a large round strick. and imagine straight strips being drawn down that stick from one end to the other. then imagine two points being marked on the stick at different points along the strips you drew. only, you didn't draw them along the same strip, you drew them along a strip that was paralell to the one you marked on. then you draw a straight line between the first marking you made, and the second marking you made on the strip that was parallel to it.
in other words, the two points have a cambe, or hill, between them. and you have to raise you action above the hill. the string cannot oscillate inbetween the two points, because there is a cambre in the way
