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.
I think they are just trying to use one ratio for economy of scale, as the manufacturer will be likely the one putting them all together. Ie: they probably ge t a better price ordering 1000 3.55 gear sets rather than 50 of this and 50 of that etc…