Quoted:
The RCR did move the window up a bit, however in doing so it makes the bottom of the window level with the top of the body back where the elevation adjustment is.  On the RMR, the bottom of the glass actually sits lower than the high spot on the back of the body, and that high spot is the part the irons would have to clear to be usable.  

It's hard to see exactly here because of the lighting and angle, but the height of that rear body is the same (or damn close) between the two.  So you should still be able to alight the irons if your rear clears the rear of the optic, the only different is that in the RCR you'll probably see a bit less of the lower half of the front sight through the optic because the window is higher, but you should still see enough of the top of the front sight to make them usable.

https://www.ar15.com/media/mediaFiles/157876/1000004435_jpg-2921329-2921543.jpg

Quoted:
The RCR did move the window up a bit, however in doing so it makes the bottom of the window level with the top of the body back where the elevation adjustment is.  On the RMR, the bottom of the glass actually sits lower than the high spot on the back of the body, and that high spot is the part the irons would have to clear to be usable.  

It's hard to see exactly here because of the lighting and angle, but the height of that rear body is the same (or damn close) between the two.  So you should still be able to alight the irons if your rear clears the rear of the optic, the only different is that in the RCR you'll probably see a bit less of the lower half of the front sight through the optic because the window is higher, but you should still see enough of the top of the front sight to make them usable.

https://www.ar15.com/media/mediaFiles/157876/1000004435_jpg-2921329-2921543.jpg