I don't think the offset has any issue with it, possibly, but unlikely. My fitment is very flush and they are very concave. Normally you would think the spokes might hit the caliper or something else. What they are say is the parking brake is actually gouging the inside barrel of the wheel.
I don't think this is a Signature specific issue hence the reason I didn't mention brand in my post. I did reach out to Jamie to get feedback and he hass been nothing but helpful. You couldn't ask for more TBH.
So a few things don't seem right but I can't investigate more until I get the car back. In general 21's should have at least a 1/2" more clearance than 20's. Even if the barrel of my wheel is a bit thicker, the fact that I have a 21" should give me more clearance. They said if mounted the parking brake would actual gouge the inner face of the rear wheel barrel.
I don't see how this can be as I work through the fitment scenarios. There is one or two possible ones but they aren't that likely. So I don't want to speculate. Once I get the car back, I'll try and fit my wheels again, take some measurements and see what the issue is and provide updates. Jamie is willing to work with me to help find a solution. I absolutely don't want to go with the Zero-G wheels and would love to keep a set of Signature wheels on my car. From what I understand, there have been no issues with SV104s and already a success
Thanks, this is very helpful. Definitely tight but 21's should provide even more clearance.