There are many styles if you look at photos.
I made a pair of them a couple years ago.
I think you need to play around with the design quite a bit unless it's just for display.
For me, if it gets too long, then it seems unstable if you hit anything. Also, I like it pretty narrow where it passes between your fingers, so you can make a natural fist. You can also choose which fingers it should pass between and how you get a solid push with it. I also like some clearance so you don't have it tip and crush your fingers. The handle thickness is another parameter to explore. Beyond that, I would just draw up a dagger style of blade, although you see some with one side, or partial second side.
Please post pics, I'll be interested in what you come up with.
Another good use for scraps is a lapel dagger...