It then partly comes down to how much good audience reaction you are getting in that PAS pair, since the PAS pair will also be providing a degree of room and audience, with stereo width to it. If you just want to be able to reinforce that audience reaction you're already partly getting in the PAS pair, then a single mic dedicated to audience/ambiance will be fine. Audience reaction and room ambiance are best as wide stereo which envelops the listener, but that's a luxurious nicety, especially when dealing with more important unpredictables.
If open to playing around with that single audience/ambience channel upon mixdown after you've gotten all the more important stuff dialed in, you can try a few tricks to 'widen' it such as copying the track to two channels panned left and right, then delaying one side slightly relative to the other, or flipping polarity on one side. That kind of stuff, and the usefulness of having separate level and eq control over audience/ambiance regardless of how many channels you dedicate to recording it, is going to be maximized and made more useful by isolating it from the PA and onstage sound as much as you can. Place that mic in such a way as to maximally exclude the PA and on-stage sound from reaching it, while still focusing on the 'best, energetic and enthusiastic' portion of the audience.
I've found that when I've dedicated channels to this, arranging mics at the stage-lip or onstage, it dramatically helped to hang the audience/ambiance mics from the lip, just in front and under the stage surface itself, so that the stage itself contributes as a barrier against direct on-stage sound reaching those mics. Even using parallel cardioids facing out into the audience with their nulls facing the sound sources on stage, when they were positioned above the lip they had much more stage sound in them which limited how much audience I could add later and what I could do with it eq-wise before running into problems from stage-bleed.
So yeah, a single supercard in the center may be your best choice, blocked from both on-stage sound arriving from behind it and the PA above it and to the sides if possible.