I'm not sure if this is documented anywhere, because I couldn't find it, but with the Gen 2 micro in a LaRue LT-661 mount (the shortest of the three), I measure the center of the tube at 0.94" from the top of the rail (plus or minus a few hundredths).
On my SIG556 Classic, this is almost enough to give me absolute cowitness. I can live with it. I may investigate the LT-660HK mount, but I suspect that it may be slightly too high.
edit: Using the numbers provided by LaRue, the LT-660HK is 0.47" taller than the LT-661, so that's a definite no-go on the Sig.