...I guess that's as clear as mud!!!
It seems very clear to me, Simon...
...I wish all such "briefs" were as well described when they're posted here, so congratulations !
Sadly, your dilemma is one that I've often struck, not just in the dreaded "multi-purpose hall" such as yours, but also whenever theatre companies attempt to "break out" from their traditional proscenium "end stages" for a given "in the round" production.
While your fear of needing to invest double in order to "re-patch" between two complete "back to back" antenna installations is completely justified, the experience I've had in touring my P180 equipped systems makes me think that it'll probably be a whole lot less fraught than you think.
I'd propose that you start with just one pair of P180 paddles and a pair of 50ft LMR-195 cables.
As you're running a maximum of 12 systems, I'd recommend switching them to the more robust, four-frequency diversity RF1 scheme and conducting fully-populated walk-test trials for positioning that pair of antennae.
...I doubt one set of paddles effectively in the middle of a 100ft cable (using a T) with one end left unterminated, would work very well...
…Quite so, in fact I'd go so far as to predict a set-up like that would very likely be an unmitigated disaster !
However, I would NOT be surprised to hear that you'd eventually found a "compromise" position for your single diversity pair of P180 paddles that (using RF1) yielded solid results over your entire auditorium...
…following some thinking that's "lateral" in more ways than one.
I'm guessing that your hall's "lighting grid" only exists over the "conventional" stage behind its proscenium arch and curtains that are at one end.
Accordingly, my suggestion would be to possibly abandon this as being the primary or exclusive support for your pair of P180 paddles, in favour of experimentation atop tall boom stands possibly yielding a location (or locations) out from and along one side wall that give/s you the coverage you're seeking.
Literally laterally, ...in that both antennae may end up "looking across" the hall, or one could end up "looking along" it from that lighting grid, with its "mate" covering the hall from its side wall, almost at a right angle to the first.
Once those best coverage "spots" are revealed, I find that this sort of (relatively cheap) hardware is then handy to subsequently arrange permanent mounting: