1. If you run at Jan Heine's recommended pressures and weigh 230 lbs
ike me, handling will be unstable. The tire starts to collapse as you
lean it into corners. I run 50 psi in the front and about 55 ps in the
back and that solved that problem. The threshold of this phenomenon is
pretty sharp.

Are you sure that you're running his recommended pressures? I thought he's posted before that he runs higher pressures on pavement-only rides than gravel due to this phenomenon, and he definitely recommends experimenting with wide tires because of how sensitive their behavior is with tire pressure changes.

For what it's worth, when I ride good roads, I ride my Rat Trap Pass ELs (measure 2.1") at 40r/35f, and I weigh 170lbs. Considering your added weight and the reduced width of your tires, I'm not surprised you'd like running your rear at 55PSI for pavement, especially given that you've got narrower rims than I do (CR18 has 18mm internal width, my rims have 24mm internal width).
I often ride 30PSI or lower on gravel rides, where foldover is less of an issue because the riding surface breaks away when you corner hard. When I have them set up like that, they definitely feel squirmy in paved cornering.

2. Jan makes various claims about the tires. The ones that I can say
are true my experience are (a) the tires are very, very quiet on the
road

I'm not familiar with that particular claim, but I'd actually strongly disagree with it. My Rat Trap Pass ELs absolutely roar on good roads. Road hum is a pretty common thing with supple road tire setups.