@shibao @Rocc @glow

I built a Glock 19 using a Brownells brand slide, native milled for RMR. I bought somewhat tall sights for it. Not super tall, but taller than normal. But the RMR sits so deep on that slide that sights obscured a good half of the lens, The RMR-to-RMR plate lifts the sight just enough so that I can see the dot with something like lower 1/4 to 1/3 co-witness.

Reptilia intended that plate for some weird-ass shotgun application. It even had recoil pegs. And apparently it was so popular that they make a whole array of them in various colors and thicknesses:
https://reptiliacorp.com/product/rof-riser-for-trijicon-rmr/

Today I would just print a little plate from Nyon, perhaps with a little spacer that transfers the recoil instead of the pegs. But that was then.