Designing a stitching clam

I was listening to a podcast where Philip mentioned how so many tools were built by people who had never worked in the craft and how obvious this was the first time an experienced person tried to use them. So with that in mind, I've never used or even seen a stitching clam in real life but it seems like a great idea to try and build one ;)

Actually, for full background, I am trying to order some overseas tools and it seems like I'll have a few weeks to wait until they arrive. In the meantime, while watching the videos here I figured I could use some woodworking experience to build a few things.

My question is, for those who have actually used a clam, is there something you'd ideally tweak about its design? I'm fairly tall (6'4" / 193cm) so I'm not sure how an off the shelf clam would fit me. I'm making mine adjustable in height within a range of 36 to 51 inches (90cm and 130cm) approx. The Blanchard ones appear to be 105cm and 130cm. When I take a scrap board and lay it across my leg it seems like something around 48" (122cm) would do it, but I'm not entirely sure where I should target the jaws of this thing being. In some pics I see people with them low, close the leg, and in others it seems much more upright by the chest. The Fred Moreau one that people rave about seems to be used very upright. But Philip seems to have his much lower.

Also, if it matters, I plan to work on small items for now - watch straps and wallets, so I don't think I need huge capacity. The jaws I have drawn below are about 13" deep and close to 3" high.

This of course is why I'll build the initial one from plywood before committing to final dimensions, but any input at this stage would really help!

Thanks, Jeff