Going back over this with great interest, but slightly thrown by what may be a misprint:
by limiting the Ug to 0.7 it helps to ensure that the manufacturer does not place undue emphasis on the design of the frame
If you confirm Mark that that should read 'design of the glass', then I'm happy, otherwise baffled!
The attached is what we're talking about?
I also had a question in my previous post on this thread, previous page.