Sytong HT70 - Return to zero issues

Morning everyone,
Just after a bit of advice from any Sytong users out there.
I swap my HT70 back and forth a lot between my 22 and 308, and cant seem to get it to return to anywhere close to zero when remounting (up to a foot out on windage at 200m on the 308. Elevation is usually pretty good, within an inch).
I have the Pic rail marked so it goes back in the same spot each time, and always torqued down to the same setting.
At first i thought i must have been forgetting to change the zero setting back to the correct gun, but after double checking, still having the same issue.
When I refit my Element Helix back on the gun, it always returns to within an inch, so i dont think theres an issue with the Pic rail.
Anyone got any tips?
Cheers

Have you tried removing, then putting it straight back on, then see if that causes shift. That could then identify that there is slight movement in the mount.