The Contax AX is a fairly unique camera that has back focus within the camera body, that has 10mm of travel. I have never had one and don't know the limits of the system; for example I don't know if it can bring the film closer so that it focuses a lens "past infinity." However, this extra degree of freedom means that one could have a lens that has some focus offset that the AX compensates for, but the Aria cannot. More detail is needed to diagnose the problem - what disagrees, the lens focus scale, the ground glass, the focus at the film plane? What focal length lens? Can it be focused at 1 or 2 meters but not at infinity? and so on.