Recording a choir is a lot of fun - can also be a lot of work to get it right.
A couple of observations...
First - the ORTF configuration is meant to capture both volume and time (read phase) differences. So especially at such a close distance I'd expect phase differences - not issues<G>. I prefer coincident configurations, but when I use ORTF I use it at some distance from the source.
I prefer (at least these days) either Mid/Side or Blumlein configurations for stereo recording. I don't get the same depth of image, but i get great mono compatibility, and very repeatable results.
I also tend to shy away from large capsule cardiod microphones when recording spaces. I've never been completely happy with the results. I do lean towards cardiod patterns, but I prefer small capsules at any distance.
Ultimately, and I don't say this to sound simplistic, it comes down to how the choir sounds in that specific space. Have them sing and walk around the room. Get a really tall boom stand and place a stereo pair (coincident or not) way up high and give that a listen.
Without seeing/hearing the space and the choir I can't get more specific than that, but I can tell you what has worked for me in the past. This was for a 40 plus piece children's choir in a large, stone church.
1) a Blumlein pair using a Royer SF-12 stereo ribbon microphone was placed about 20 feet back, and about 15 feet up (maybe higher, it was as high as my stand would go.)
2) a coincident pair of Earthworks SR-77 microphones was placed about five feet behind the conductor and about 5 feet above her head.
3) I also placed a pair of Sennheiser MKH-405s about 10 feet back and at the extreme sides of the church. I ended up not using those tracks, they didn't provide anything I didn't already have.
Your mileage, of course, will almost certainly vary!!!