I completly agree that the lower shouldn't matter, the sighting is done with the upper portion only. I searched BushMaster's site and found, (what I believe), Matt was talking about:
Article # 153 Will the Bushmaster V-Match upper receiver accept the Colt Detachable carry handle? Answer Our V-Match (flattop) receivers will accept the Colt carry handles - however, the Colt barrel as installed on their upper has a front sight that is about .040" higher than mil-spec. This can cause an elevation problem when using mis-matched parts. The Colt handle will only work with a Colt match barrel. The Carry Handle that we are introducing will work with anyone's barrels (except the Colt Match barrel). Call us at 1-800-998-SWAT to order the new Bushmaster Carry Handle.
Matt may have said "lower" but ment to say "handle", or Matt said "handle" and I heard "lower". Page 64 of the BushMaster catalog for sight # 9349056-m even states it is for the Colt removable handle. This makes me think that he was referring to this.
YELLOWV, Thanks for the help, I do appreciate it. What I posted above is just to be fair to Matt in case I had previously misquoted him. I have not shipped the rifle yet so I will call Leon on Monday and ask him to ship the taller sight post and try that first.