centering nozzle/tape shot 1mm in diameter CL-6

Hi. I have a new problem. Since trying to swap lens from 5" to 7.5" (and back) I have not been able to
center the lens/nozzle. The beam appears to be centered but because the hole it makes at 50 watts is
at least 1mm in diameter it is hard to determine. I have tried with various nozzle diameters and moving the focus up and down
and the results are always the same, 1mm hole in tape. I have consulted many experts and all are stumped
(at least via phone/email). Anyone have an idea on this. The laser is a 2 kw cinci from the early 2000's CL-6/fanuc 160iL.
It was perfectly centered and focused (not by me, prior to my arrival) and then change to 7.5" lens and
has been giving me issues ever since.

Thanks,

Allan