I'm not sure I can help too much. I agree with all you suggest, and that's all I could suggest myself.
Polished round pontil marks are not known to appear on early Aurene, but the way the colours are worked, it looks far more IoW than Mdina.
How wide is it? I was wondering if dimensions might help, given IoW were a bit more restrictive about size, although I've got some unusual sizes of Aurene cylinders - and unusual colour combinations. The cylinders, especially if big, were more prone to experimentation.
I have two unusual Tortoiseshell cylinders - both have a very yellow colour of background glass and the way the design is executed looks the same, but one is Mdina (Marked on the base) the other is early IoWSG. It's got a (very squished) flame mark on a button. Just to show you how very, very similar early IoW and late Harris period Mdina are.
I do have a couple of massive Aurene cylinders, they're (roughly) 10.5 " tall and 4.5" wide. (I can't find a tape measure, not even the one the cat shredded and have had to estimate using my hand span, which is 7.5".)
Would you like pics of them? They're fairly standard Aurene, though, nothing weird. My weird bits are inbetweeny and wide.