Hi,
aea r84 are ribbon mics, in germany avaible through the guys at morphon (
www.morphon.de). And I'm really excited about the mics.
They have a very smooth but detailed sound picture. I tried it with a blumlein, the two mics on top of eachother, and put the choir around it. You need to adjust the voices by letting them step forward or back.
Try AB also with small capsules and check yourself what you like better. I usualy do that kind of recording with XY.
I don't know what you mean with the innertube inside the choir, if you mean between the lines, than I guess that it doesn't make much sense and you will get phasing hell when you combine it with the main mics.
I would try to get the sound out of the main mics, and use aditional mikes as spot mikes for safety and get a bit upfront.
2.50m is not very high, but as I don't know the room I don't know, but hear about any pressure fx when you put the mics close to the ceiling.
wolfgang
toolhouse studios, germany