There must be a reason why most armies have dropped the whole poncho idea and replaced it with a dedicated set of waterproofs and a tarp (basha).
Probably the reason for dedicated waterproofs isn't quite so important for bushcraft, but the reason for the basha being that much larger than the poncho it replaces is.
That said, we used to have to fit two people under each poncho, and i survived (and that was in the day of feather filled sleeping bags and no bivvi bags). It just wasn't very comfortable/luxurious (even for one person), so in bushcraft when i can make the rules, i'd always go for a much larger tarp!