Indeed - but, as we know, that is only an issue if one is fairly 'close' to one end of the ring. Once one passes the threshold distance from the ring origin, on can put the entire 32A load at one point of the ring without overloading any cable.Exactly - using the 4mm cable rather then separate legs forces all the accessories on the 4mm cable to be artificially very-close-to-one-another on the ring even when they wouldn't be in the 2x2.5 situation.
With a 2.5mm² Method C ring, one really does have to get pretty close to one end before there is a problem - since (assuming that the circuit's design current of 32A is not exceeded) the threshold case is 27A down one arm of the ring and just 5A down the other.
Kind Regards, John