I don't understand......are they claiming that the housing itself can only accommodate one ratio and they are taking a survey of which one is most desirable OR are they asking about ratios to know which ratio of gears to offer?
I don't know why a carrier would only allow for one single ratio. I do know that the taller the ratio, the larger the pinion gear and the clearance there is tight.
They are trying to offer the option they think will appeal/sell the most, while offering ONLY one pre-assembled chunk. They don't wanna stock a whole bunch of options, and have them all sitting on a shelf.
The aluminum chunk I ordered was built per my specs. I was surprised how soon it came, considering it was a special order. (But nine inch Ford parts outnumber 8 3/4 about 10,0000 to 1)