So, what's up with the diamond shape in the counterguard?

[Hotspur]

Hi guys

I know I lurk here more than post but many topics seem to bring out the possibilities of collective thought. Mentioned in a few threads here and elsewhere are the shape found in what seems to be predominantly British made sword with a bow counterguard. Does anyone have the definitive explanation for these? Attached are a Woolley and a Thurkle. I know I see enough of them that it seems commonplace enough that there must be something to it aside from an architectural standpoint or just something to fill the space. Why this instead of a circle? Or indeed any number of other shapes?

Cheers

GC