I'm not a frame builder, but I have some experience with small wheeled bikes. I'll offer a few observations.... mostly anecdotes.

With the 'standard' size wheel (26-29 inches) you have a certain amount of "wiggle room", in which you can vary both head tube angle and offset a little one way or another for subtle changes in handling, while always remaining in the 'acceptable' range. The point I want to emphasize is that as the wheel size decreases, the "wiggle room" decreases. The tolerances are a lot smaller.

Alex Moulton was the principal prophet of small wheeled bikes starting about 60 years ago. I can't find it now, after a short google image search, but somewhere on the internet is a photo of an experimental Moulton bike from about 60 years ago, that had adjustable fork rake just as was described above. Based on what he learned, he introduced the F-Frame bikes in the early 60's. These had 16" wheels (specifically 16 x 1 3/8, 349 mm bead seat diameter). I have had a couple of those over the years, and I found both to be extremely twitchy. I could not ride either one with no-hands. I never liked the way they handled. I cannot now recall whether I tried riding either one no-hands with a heavy load on the front rack (they had an excellent frame-mounted front rack; so they were definitely designed for a front load). I found it odd that Moulton had considered this factor carefully, and arrived at a result I don't like... can't please everyone, I guess.

Raleigh answered the Moulton challenge first with the RSW-16 and then with the Raleigh Twenty. The former had 16x2 wheels (305 mm bead seat diameter, but overall diameter about the same as Moulton's wheels). My wife has one, and I find the ride to be very twitchy; I can't ride it no-hands (but it is much too small for me anyway, and this is a factor). She doesn't ride any bike no-hands. I've also ridden a Raleigh Twenty, with the same result: too twitchy for my taste.

I remember reading, presumably somewhere on Bikeforums (presumably in the folding bike subforum) a post (from about ten years ago, I'll guess) by John Forester, in which he described straightening the fork of a Raleigh Twenty, reducing offset slightly, with the result that the handling was improved. But as I say, I can't find this post anymore. I did try straightening the fork on my Twenty, and it helped.

I used to ride a Counterpoint Presto! recumbent, with 20 x 1 3/8 wheels (451 mm bead seat diameter) and that, too, was too twitchy for my taste.

Then again, when my daughter was an immortal and unbreakable ten year old she had a piece of junk 20" bike that I pulled out of a dumpster for her, and she could ride that thing all over the neighborhood with her hands in the pockets of her jacket. It was perfectly stable, and she could steer around corners etc by balance. My current folding bike (a Downtube 8H from 2015, I think) is stable and rides fine no-hands. Both of those bikes have 20" (406 mm bead seat diameter) wheels.

And for several years I rode a folding bike with 16" wheels, the same size rims as the Raleigh RSW-16 (mine was a Downtube Mini from 2007). It was designed for 16 x 1.75 tires, but in that configuration the handling was a bit twitchy, and I could not ride it no-hands. I found by putting the narrowest available tire on the rear (1.25") and the fattest one on front (2") I shifted the head tube angle enough that I could ride it no-hands without any difficulty.