It might be worthwhile to look at Paterek, Talbot and the Proteus manual. Just treat them all with skepticism. I'm sure Dave Levy has more experience and knowledge than all those authors combined.
I wouldn't buy Talbot, hopefully OP can get it at a library. Some versions of Paterek are available online. So is the Proteus manual. I don't know if you can find the CONI manual online, it's pretty expensive to buy nowadays.
Delving* deeper into bike steering geometry is an interesting idea, but in the end there's a reason why upright bikes are designed with a relatively limited range of steering geometry. Probably best to try to understand what that range is and how you want to the bike to handle. I always recommend sticking with something that's well-tested for an initial few frames.
*apparently, recruiters think that if you use "delve" in your resume, you used AI to generate it. I swear no intelligence was used in crafting this post.