Is there any good rule of thumb for minimum clearance from tire sidewall to strut?

Installing 225/45-13 Hoosiers for the first time on my Scirocco and not sure how much spacer to run. Obviously I'll install and check static gap but not sure how much tire deformation to allow for. Area where it would contact is smooth so light contact probably wouldn't be a big deal, but I'd still like to get it right first try.

Current setup (Kumhos) has about 3/8" clearance and does not rub. How much closer is it safe to go?

Thanks!

Al Seim
www.actdigital.com