Hiya riffraff,
yeh numbers is a big problem, as you say it depends on location and conditions. The caves for example is loose under foot, so therefore even small groups would make noise on evps. I do think all evps should be done with no more than 3 people in the room, in a place like the caves manybe groups of two in other parts furthur up also recording at the same time.
In a house investigation, like plumstead we only had a small team and it was almost too many... Which is why im looking at getting as many locations sorted so the group can be spread smaller over a number of locaions thus improving the evidence...
You saw what happened when twopeople waked throught the caves it caused them to be more bold... so i also think its good for the spirts and evidence.