even way off center, you can pick up plenty of the other stack, you'd be amazed at how directional the mics really are...you will certainly get more of one stack, but it won't be like a mono blob or anything...what i do off-center (and i don't actually think too many others do this, but it's worked for me so hey, whatever), is orient the center axis between a stereo pair at the area between the stacks and bring the included angle in a little bit from 90*. so with cards, i'd end up with about 20cm spacing and about 70 degrees of spacing...it works nice and you still get a good stereo image, a little narrower than with 90*, but it will still be very listenable. another option i found works well is X-Y oriented between the stacks...i wouldn't do ortf from far off-center