This excellent site by Anatoly Zak, shows lots of things about (notably) the Soyuz spacecraft.
When the Soyuz T10-1 had to use the launch escape tower, not only the 2.9 tonnes crew module was ejected, but also the 1.3 tonne orbital module (on its top). I always thought something was wrong: why put an orbital module above a crew module? Why Korolev designed it that way?
It's impossible to add one more astronaut in this configuration.
Was it because the crew module could not have a wider diameter than 2.2 meters (same diameter as the last stage), and aerodynamics at re-entry forced to choose a bell-shaped capsule? Was it because the parachute couldn't sustain more than 3 tonnes, meaning equipment for spacewalks , docking with a lunar module or a space station, toilet, food, rendez-vous antenna needed to be put in a separate section from the re-entry crew module?

It's interesting to see that the Chinese have adopted the same philosophy (separate orbital module, also in front of the capsule).

But this prevents the capsule from taking a larger crew and it adds more weight to the Launch Escape System's job.
The Service module+crew module+orbital module weigh 7,1 tonnes.

The Apollo Command Module "alone" weighted 5.8 tonnes.

Raoul