Playing with shader mixer (Patreon)

Tried to implement Iray 2020 features. Sheen works fine but multiscatter doesn't work, I've tried different BSDF w/o multiscatter but the result is always the same, i don't know if it's a bug of this version or what. One way to reduce the problem of dark edges is to reduce the maximum reflectivity and compensate for it by raising the base reflectivity, but this only reduces the problem and does not solve it.