After watching that vid, I'm sad to see that it's no longer being developed and that the devs didn't leave any open source behind. :( That would have been really cool to try out.
Good rule of thumb to capitalize letters with circle is just to make the circle as large as it can go within the keyboard area. It doesn't have to be centered around the key, just needs to start on the key. For center I usually just circle down from the key as far as I can.
I'll vouch for Koboldcpp. I use the CUDA version currently and it has a lot of what you'd need to get the settings that work for you. Just remember to save what works best as a .kcpps, or else you'll be putting it in manually every time you boot it up (though saving doesn't work on Linux afaik, and its a pain that it doesn't).