I have a Sabre mid-length upper with a Troy BUIS. My front sight base is marked with an "F" but the front sight post is cranked up pretty high. I'm trying to figure out what is wrong here; is it the front sight base or is it the Troy BUIS?

Did Sabre use a standard FSB and just mark it with an F or does Troy build their BUIS to match the original height of an A2 upper?