If one wants to increase the size of the Soyuz return module, one will have to :
1) drop the orbital module which has the equipment for docking with a station (hatch and radar for instance).
2) increase the heat shield surface because the bell shaped capsule is still the prefered one, unless they change the whole thing, which the Russians never did to such an extend.
3) Increase the parachute volume (and storage space) and rocket fuel for the last second brake.
4) the service module would also need to take more fuel because it would have to slow down a heavier mass than it currently is the case as the orbital module is discarded before the engines are turned on for the last time.

I'm sure Korolev thought the orbital module solution was a way to reduce the weight of the return capsule to the minimum possible; he thus transfered part of the equipment to another e, non recoverable module.