Most, if not all, of the back views I've seen from the 14th century suggest permanant attachment of the guige. I don't think i have any in scanned in unfortunaly
Mine will ahve a fixed attatchment.
I got those rings in by the way. PM or e-mail me when you get a chance.
Check Bobby de Shurland's effigy in Orkney. He shows at least two buckles on straps behind his shield and at least one of these straps is a guige. Guiges generally need to be adjustable, and if they aren't sufficiently adjustable, there's going to be some buckles added.