Yes, googling suggested that this goes through bcrypt on Windows. We don't have an RNG implementation in bcrypt though (we do it the other way around; bcrypt calls RtlGenRandom()). I guess we could add a Unix call in bcrypt that calls getrandom() in the GnuTLS backend and implement BCryptGenRandom on top of that. The downside is that this depends on having GnuTLS available, although missing it breaks Wine in many other ways as well.
Anyway, I thought that until we figure this out it should be fine to bump the buffer size.