Thanks for the idea Michal. Sorry for getting back to you late.
The way you described it I would require multiple Forests which I'd like to avoid.
I'm trying to use FP to simulate large scale crowds. For example I want to pose a walking group of 3,4 or 5 people, standing groups of different sizes, then distribute those posed groups but each time they're repeated, I want FP to select a different model from a particular forest set that contains only walking people, or a forest set that contains only standing people, so that the same group of people aren't repeated throughout.
Does that make sense? If I use the triangle geometry in Reference mode, I would need a Forest for walking people, another forest for standing people etc