Here's an interesting approach:
So far in this discussion, it has been assumed that the Soyuz-class is a derivative of the Miranda-class. But what if something else entirely happened? What if the Miranda was derived from a design ancestor of the Bozeman / Soyuz, originating during either the TOS or pre-TOS era? We have no idea what the Soyuz looked like (or whatever it was derived from may have looked like) back then; for all we know, it could have looked (at least a little) like Forbin's Minmus or Starscape's TOSified Orion or Tereshkova or something else.
Here's a design possibility: let's assume for a moment that, like Forbin's Minmus, this ancestor did not have the bustle-back bloated saucer like we saw with the Reliant/Saratoga. Let's consider that the saucer was unbroken, except, maybe, for a thin aft wedge, like a cross between the Bozeman's expanded tail and Forbin's Minmus. Let's call this ancestor design a pre-refit Soyuz, just for sake of argument. And let's assume that this was the original Federation saucer-over-nacelles design. Was it called Soyuz? Maybe, or maybe a different class name entirely. Soyuz, Miranda and perhaps over ships would've been derived/refitted from this old design.
The reason I suggest this is because the Soyuz-type design seems bulky; perhaps the ancestor design was bulkier, just as the Enterprise's older bridge module was bulkier pre-TOS.
So far in this discussion, it has been assumed that the Soyuz-class is a derivative of the Miranda-class. But what if something else entirely happened? What if the Miranda was derived from a design ancestor of the Bozeman / Soyuz, originating during either the TOS or pre-TOS era? We have no idea what the Soyuz looked like (or whatever it was derived from may have looked like) back then; for all we know, it could have looked (at least a little) like Forbin's Minmus or Starscape's TOSified Orion or Tereshkova or something else.
Here's a design possibility: let's assume for a moment that, like Forbin's Minmus, this ancestor did not have the bustle-back bloated saucer like we saw with the Reliant/Saratoga. Let's consider that the saucer was unbroken, except, maybe, for a thin aft wedge, like a cross between the Bozeman's expanded tail and Forbin's Minmus. Let's call this ancestor design a pre-refit Soyuz, just for sake of argument. And let's assume that this was the original Federation saucer-over-nacelles design. Was it called Soyuz? Maybe, or maybe a different class name entirely. Soyuz, Miranda and perhaps over ships would've been derived/refitted from this old design.
The reason I suggest this is because the Soyuz-type design seems bulky; perhaps the ancestor design was bulkier, just as the Enterprise's older bridge module was bulkier pre-TOS.