Yes, that's a good point (after remembering you playing around with making superb armour by spending a season repeatedly rolling a finesse stress die until you got Excellent+27, arguing reasonably plausibly that the ingredients should be reusable in this case, then suggesting capping it at +4 instead). That or stopping it being stress - I can't remember what you'd done to it to make it be so now. Was it just mastering the spell, and then extrapolating that "with a stress die but no botch dice if relaxed" applied to the finesse roll as well as the spell casting roll?
So the cap would be that the Total Bonus couldn't be more than Finesse/3, for consistency with the limit of Craft/3 usually?