FF3 here. Check out the MaddMacs base for them.
I put one of the Maddmacs bases on my MKIV along with a Crimson trace RDS. My goal was the lowest mounting possible and hopefully co-witness with the sights. It worked just as I'd hoped. I have a rail on my Buckmark and always have to hunt for the dot because it's just not intuitive setting up that high. Not a big deal when just punching paper off a bench but annoying when informal plinking.