I think the highest gain screen designed for UST that I've seen advertised so far is .8, but I'd be suspect if that claim is real, as most others that I've seen are .6 or .5 and I think there are only a handful of actual manufacturers producing UST screens.
XY Screen have a PET Crystal High Gain(0.96) very good screen for the UST projectors.
Do you have a link? I just looked at their site and all of their UST screens that I saw are listed as .8, with the exception of a rigid Fresnel screen designed for UST projectors that is 1.2. And it tops out at 100"
"F7USP 2.35:1 Cinemascope format High gain 1.4 Ultra Short -Throw Ambient light rejecting zero edge fixed frame front projection screen is the newest nano ALR fixed frame screen that uses the PVC crystal 1.4 which is tailor-made for ultra short throw projectors. It adopts trapezoidal optical structure and directional coating tecnology, which makes it overall performance slightly better than the PET crystal anti-light curtain."
Anyone care to be a guinea pig and try it out and report back to us? LOL! But it's 2.35, which means black bars on the side for a lot of content, right?