You really don't need a spacer for the Eotech...it sits at the PERFECT height for an instantaneous sight picture when you bring the rifle up to any normal firing position. The intensity of the outer/inner ring is such that it will completely overshadow the front sight, if you turn it up even close to all the way.
With a #40, you will have an ideal optics/buis arrangement, IMHO.
BTW, I just got my Aimpoint Comp C. I don't know how much brighter than the Comp C the M/ML2s are, but I am underwhelmed by the brightness of this sight. Maybe I'm spoiled by the incredibley bright 10moa dot my ProPoint3 Plus has, but I can see that in a bright outdoor setting, this dot is gonna be hard to see.
This was a gift, and I couldn't really ask the person to shell out any more money than they did...but I will have to think about whether to keep it or not based on the lack of brightness, to be honest. I'll head for the range tomorrow, it's gonna be nice and sunny here.
If I could find a better mount setup for the ProPoint3, I'd be very happy...that's the one drawback to that sight so far...really cheap rings, and it's a 33mm tube...so I can't find anything else that will work.
NO such problems with my Holosight...that is one bright sight. You will love the Eotech, I'm sure.