I have checked and re-checed and others who I shoot with are saying its dead on and not canted. I have spun that scope rt and left and it always comes back to zero. every time.
I'm talking about "canted" at the bases or mounts from being bad quality bases or mounts, or inadequate installation.
As an example:
I have Burris Signature Zee rings on my Howa. Say I were to use the inserts that "cant" my scope giving me 20moa more in elevation adjustment. Now say I installed them rotated 90 degrees, making my scope "canted" horizontally instead of vertically; I would get the same result you are experiencing.
I would think if your objective lens is centered over the bore, your horizontal POI would remain constant.