I understand your logic and your method but...
Rangefinders and cameras are adjusted on a collimeter to infinity and ground glass tested throughout it's range of focus to be sure the film n viewfinders agree.
Before adjusting anything...
Have you checked it on a collimeter to be sure infinity is in focus on both cameras?
Taking a lens off one without moving it is not a test of accuracy.
Viewing a target side by side of identical cameras is not a confirmation, individual ground glass test is.
After adjusting it... Have you actually tried putting a ground glass on the film gate to see if infact the image is in focus n still agrees with the RF?
Since you say both cameras are identical... are the backs exactly the same? Check to see if one has a diopter of a different strength?