Sorry to resurrect this old thread, but I'm dealing with just the same issue here. And Shaggy never got any replied in the first place...
Until now, I've always ran my AT853 cards in XY configuration, with the same "mount".
But I picked up a an oversized K-ng-l knockoff that will more or less allow me to run ORTF, with the mics in each corner of the brim.
So I'm modelling on a DIY bar to get the spacing and angle right.
Is ORTF considered to be the optimal configuration for cards mounted in "constricted places" (given the limited width allowed)?
And would it still be useable if I switch to my subcards or hyper caps? Or should I space them differently?