Image position follows the tweeter, as I found out when one of mine failed.
You’ve established that the issue is somewhere before the phonostage, a dameged cable with a higher capacitance on one channel might be involved but I think it a long shot. What happens if you swap channels at the cartridge tags and the phonostage input?
Try another cartridge.
How are you setting bias? If you do end up sending the blackbird back to Soundsmith get them to assess the wear on the stylus and condition of the suspension. This can tell you if you’re getting it close enough.
