Here are the 4 different types of ascenders. They are built by adding an extra line following the right hand side fishtail to the waistline, then placing the pen on top of that line and performing a pen twist. (and maybe a little bit extra to touch up)

I've measured the thickness of the ascender at the top as compared to it's width below the waistline. It's in proportion of 4: 3.

I've gone back to the graphing of the letters A-L, and re-done the ones with descenders. I'm using what seems to be my favourite version. :-