Question:
if your water is very very soft, such as using untreated RO water, this could severely diminish the crema you are getting, regardless of the beans you use.

Answer: When I attended the SCAA e-member thingie in Long Beach in July, there was a speaker from Cirqua who was touting their customized water treatment system. I was extremely skeptical of the impact of water hardness on crema production and thought it was just self-serving nonsense. Subsequently, however, I have made the DEFINITE Observation that the crema quantity I get with my softened water (<1gpg) is quite a bit less than I used to get with the tap water slightly softened with the hose-end softener from my older Cimbali Jr. pourover (vs. the new rotary that is plumbed in on the softener). The difference is so obvious, at least to me, that I don't question it. The old hose-end water started out at 11+gpg and ended up (I'm assuming) around half that. The new water (off an undersink resin softener cartridge) is much softer (<1gpg) by test strip.

if I were to use extremely fresh (~2day old) beans in my old Jr. with the harder water, I would get (and did get) so much crema that the it wasn't "practical" to use those extremely fresh beans -- they needed to b e staled a bit, intentionally, to use your terminology from earlier posts :-) What happened when I use 2 day old beans in the old Jr. with harder water was that I got 90% crema in the cup which collapsed almost immediately making the determination of shot volume and when to end the shot repeatedly almost impossible.