Jacques de Baerze and St. George

Duke Philip the Bold commissioned a triptych for his chapter house for the Carthusian order in 1390. The carvings for this triptych were done by Jacques de Baerze and the painting and gilding was done by Melchior de Broederlam. The St. George statue I've been modeling my armour on is part of this triptych. Here's George in all his glory:

Some details:
You can see his lance rest, and the ties that keep the avantail down.

You can see how the results of Clalibus's efforts on my version of the jupon here.
I still have some work to do to mimic the belts used in this piece. You can see the mail on the back of his thigh I've been working on.

How is this leg really meant to be strapped? It looks to me like there's a strap riveted simply to the polyen (knee cop) on the inside, and straps that go through a slot in the demi-greave and greave like we see in the Chartres examples.

I'm curious about exactly why they'd configure it this way. Why do the slots for two of the straps, but not the third? Does it get in the way of articulation somehow?
Other details of the gauntlets and helm: