I use the Herbies II in combination w/ the isoplatmat. This subject has been covered here before, ad nauseum.
The isoplatmat sits on the outer raised rim of the platter of my 1200 MK II. This means that Herbies if used on the platter w/o any isoplatmat will extend up and over the rim and will require an adjustment in VTA which is easier w/ this tonearm than any other I've seen.
The thickness of the mat is only incidental. Its the fact that the mat overhangs the raised rim of the platter. The diameter of the mat actually is the critical dimension. The guy in the UK, Dave Cawley was cutting down the mats he sells, so that they wouldn't ride on the rim. They looked suspiciously like the Herbies otherwise, at a large increase in price.