Great product for stiffening the AR’s upper and lower make a solid platform but I am not sure it helps accuracy.  I don’t know about low shelf and high shelf (I am fairly new to ARs) but I have two now.  In my Bushmaster NM the accu wedge fits just right with a little bit of pressure to close.  In my brand new White Oak Arms upper and a RRA lower, no way will it close.  I will try the trimming method other have mentioned here. For the $s, this wedge really does eliminate an annoyance and a when a man has confidence in a gun he will shoot it well. I gave it 4 stars because they don’t tell you about the low/high shelf thing and the mfg that have which set up.