Radial clearance, belt drive front pulley

After using my Maney belt drive for a short while this year (lovely bit of kit, its a pity to hide it behind the primary cover!), when I removed the outer cover, I found a lot of rubber dust and particles everywhere. At first I thought this was the belt tending to run askew, but on closer examination, it turns out that the back of the belt has been rubbing on the stator supports.
When checking it, there is probably 0.5 - 1mm clearance, but when everything is whirring round at 6000rpm, obviously this is not enough.
I've not seen any mention of this problem before, so I was wondering if this was a first?
What sort of clearance should I be looking for - any ideas? I don't want to remove too much material since the stator studs do not seem to be massively over supported.

I noticed that when fitting my Maney belt, I removed some material as you mention and all was well. Can’t give you a measurement though, I just removed a bit till it ‘looked ok’.