there is a 2" block just forward of the reciver that is bored 1" as my barrel increasses in size after the trunion. the block is the same width as the reciver every thing a 1/4" forward of the barrel pin is mounted to that block. I cut the buttom of a RSB off and welded it into a milled slot on the block that is pressed on the barrel then I milled the top of the RSB off and welded in a plate that extends back ofer the reciver about 2 inches. I then screwed down a solid steel rail i milled and then tempered to that.the block is bressed tight to the trunion face and was even lapped, I pinned it with two pins.
I seriously doubt you could get .00000001 defelection between the block n the barrel and trunion. how ever the entire RSB/optics mount is still fastened on the barrel only. ill try to get a better picture of it.
MY therory is that all barrel harmonics/movement are forward of the heavy block presses tightly against the trunon face. The scope is mounted to the closest edge of those harmonics and if the barrel walkes when it gets hot the mount will follow it slightly and maintain a POA. the reciver stock fore grip ect has no factor in maintaing POA, those parts can affecct how the round is seated in the chamber and affect accuracy but the scope is still pointin the same place evey time. (AT LEAST IN THEORY) I shot 10 shot groups a quarter will cover at 200 YDS so so something is working right.
I cant wait to see how your mount on a milled reciver works out I think it will be just fine.