Re: Which mount for 1-4x on my AR?
I have had an SN4 and both USO and LaRue mounts for it.
Not to be a smartass, but the decision should be based on your cheekweld, not clearing the BUIS.
Think about it, you are talking about a $1000 optic (that all but eliminates the "backup" need by its reliability) in a $200 mount. go for what works.
If you have high enough cheekbones that shooting through the iron sights gives you a good cheekweld in all positions, go with the USO mount (they are 1.2" high, which is the same as irons. If you get in comfortable firing postition with your eyes closed, and open them to find yourself looking over the irons, get the LaRue (most LaRues are 1.5").
If I recall correctly the only BUIS that fit under a USO SN4 in USO Posi mounts that I had was a KAC 300m.
If you go LaRue, you won't need the SPR-E, I shoot NTCH and was just fine with the regular SPR as far as eye relief is concerned with a SN4 (the E may get you too far forward).