Did you ever try the LMT Enhanced Carrier in your SR-15? If so, I'm curious how it worked out for you. I've often wondered how well it would, or wouldn't, work in a 14.5" or 16" SR-15.
This carrier was originally designed for use in 14.5-16" guns utilizing carbine length gas systems which tend to start unlocking the bolt while chamber pressures are still very high. Non-SBR SR-15's don't have this problem. The extended length gas systems allow chamber pressures to drop considerably before the bolt starts to unlock. I'm wondering if it would bleed off too much gas too soon, not allowing the gun to cycle or lock back, especially with lower powered ammo such as PMC Bronze or even steel case.
And I think most who posted in this thread missed the point of your question. Unlike a standard mil-spec bolt carrier, the front face of the LMT E-carrier isn't flat where it contacts the barrel extension. It has a tapered extension that protrudes forward. This extension is there to provide coverage of the extractor pivot pin, which is pushed forward on the LMT Enhanced bolt, much like the E3 bolt. The outwardly tapered extension at the carrier face is supposed to seat inside the mouth of the barrel extension, which is tapered inward on standard extensions.
To answer your question, the mouth of the E3 barrel extension has the same inward taper as a standard extension, so the LMT carrier shouldn't create any unwanted issues with contact between the two components.