Again on PREDELAY: Down the botom of the settings is one called 'pre-reverb' is that what I want to set to 50-75 mseconds?
That's the one but rather than that let's take it a step further.
Pre delay isn't the primary definer of room size. In larger verb presets it can already have before most of the early or main reflections gaps built into them. Think of it as big spaces by design having the early stuff set back (in time and/or level.
What would be a good trial might be to pull up some medium to small rooms (or plate) and where reflections tend to be closer and shorter. These tend to combine with the source and set it back into the verb space by nature.
Beginning with decent amount of 'wet and a zero predelay on a kit for example, adding just a few ms of predelay will let the kit move forward' ahead of the verb some.
Anything from a couple of ms to 5 - 10 -15 will have more of that 'move the room back effect (source forward', same same.
-The short delays/reflection combine in our ear as one with the source (Per Haas.
-Instant depth/clarity control.
Out further, is in effect setting the walls back into audibly delayed gaps, or can even be timed to tempo like delays.
The sane stuff applies to large spaces, it's that as the reflections are (or can be) already set back and/or spaced out as well (density control), the predelay 'numbers = time of effect' aren't necessarily quite so straight forward.