Based on today's range trip, I'm thinking that the T1 doesn't make a great match with fixed irons due to the small tube. It's now matched up with Magpul BUIS on my SBR and the C4 sights are on my 16" carbine with an ML3 in a LaRue LT-150 mount. One thing I noticed while swapping components is that the LT-660 puts the centerline of the T1 at the same height that the LT-150 puts the centerline of the ML3. The T-1 has a smaller-diameter tube, so it blocks out more of the sights.