Did you shoot it with the factory original sight,,and if so did that sight require adj to the left also?

Try shooting the revolver with the factory grips,,not the upgrade target grips.
It may just be you, and the way you grip the revolver, pull the trigger, ect that requires the sight setting as so.
The oversize grips that are on it may be inflicting some influence on that.
Try it w/o them and just the factory grips instead. See there it groups w/o any sight change.
If the group suddenly goes somewhere else, I think you have an answer, or at least part of it.

Look at the front sight from the front/muzzle. See if the blade is straight and not canted from being bent.
A dropped revolver can bend them easier than most think. It only takes a couple .000 cant to throw groups off center. Making a rear sight adjustment necessary to bring them back on the mark.