This article has the best info I've read. I will continue to use 28mm tires on my BTLOS hookless 25mm IW rims. I've tested setups to 85 psi with no blow offs. I have used early model Michelin tubeless that were not approved for hookless for this reason - they suffer from bead stretch after 6-9 months of use. If deflated to add sealant, the beads dropped off the shelf and couldn't be reinflated with valve core in place. In contrast, Pirelli P-Zero TLR tires remain tight after more than a year of service. I briefly installed an old P-Zero with a tube and had a hard time getting the beads off the shelf when I took it off.
https://www.cyclingnews.com/features...t-your-safety/
For heavy riders who can't fit 32-35mm tires, it's probably best to stick with hooked, so you won't be buying Zipp or Enve wheels. Comparing a 31mm external width BTLOS rim to a hooked version of the same rim, the Zipp pressure calculator recommends about 8 psi higher pressure with the resulting 22mm IW, instead of 25mm. At least the pressure recommendation is well under what's allowed for a hooked installation.