Ok…so try these steps:
-if the verb preset offers diffusion and reverb, cut the verb level to lowest setting and only tweak diffusion. Many reverbs have diffusion in series AND parallel to verb, so cutting the verb will still make you hear the room. If diffusion is only in series to verb, you'll hear nothing…then raise verb level and lower its decay to about 0.1 sec. Notice how diffusion size makes the walls closer or more distant and diffusion itself will smear reflections or make them distinctly audible, provided some generous milliseconds settings for the diffusor delays.
Once the room is up to your liking…. move on to the verb! Add decay amount just about your taste. Verb size can make the ambience wider/bigger or smaller…like stretching the reverberant space about the audio source.
Last..BUT VERY important is eq! Long time ago some quality researches in natural reverberant spaces supported the evidence of no frequency above 4000 Hz in a verb. You can try this…or you can try anything else you may like, depending on what you feed to the verb. Cutting some low end may help with bass_ish sources and pianos.
After years of work with these structures I have come to the conclusion that there is no verb if diffusors are not properly and realistic_ally tweaked. That's where the space is made.
As Sun Ra used to say: "SPACE IS THE PLACE!"
Tweak on, man!