bitflipper
Isn't "depth" just an alternate label for what other reverbs call "predelay" or "early/late"? Maybe they've found an extra parameter we don't know about, or their depth control also applies a LPF or something. Won't know till we get our hands on it. I know you're looking forward to doing just that ;)
Both predelay (for which it looks like Pro-R allows explicit control) and ER levels are part of the alchemy (and EQ is also in the picture). Use longer predelay for front placement and higher level ERs for rear placement. It's not clear whether Pro-R's depth control does anything with predelay, but since there seems to be no way to control ER levels (or ER/tail balance), it seems safe to assume that depth at least has an impact on ER level.
If FF has nailed making it easy to dial in believable front/back perception ... then sweet! Can't wait to try it out.