I'm not sure if i'm following exactly. In a true unity clip-on then the thermal moving up and down with rail flex will not shift poi. Some long range clip on thermals like INOD have a mechanical elevator/erector built into the mount that you can activate for elr shooting. ( increses cant down of thermal by 20moa for example. That would not change your poi..... only allow for more screen to be usable/visable for your day optic erector when dialing. When a properly collimated unit is truly unity throughout the width of the eye-piece (that's key) you can literally hand hold it in front of your primary optic.On the topic of rail flex, If you zero your rifle prone then go to clipped into a tripod I have noticed that I get a POI shift. I leave the reticle turned on and "zeroed" to the same position as my day optic. This way when clipped into a tripod I can see if i am inducing any rail flex. Are you saying that rail flex is irrelevant and the POI should be the same from prone with the bipod on the fore end and clipped into a tripod just in front of the magwell?
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