For reference:

Salyut 1: Apogee 222km, Inclination: 51.6

Salyut 4: Apogee 270km, Inclination: 51.6

Mir: Apogee 374km, Inclination: 51.6

Skylab: Apogee 442km, Inclination: 50.0

Tiangong 1: Apogee 362km, Inclination: 42.0

ISS: Apogee 398km, Inclination: 51.6

I know, inclination is chosen by the launch pads which needs to reach the orbital stations. But about the height of the orbit I'm a little bit confused. Are the orbits chosen by safety, by mission design or the visiting vehicles? Which heights current and future vehicles can reach?

Is there any possibility, that the chinese decide to go with Tiangong 2 or 3 to much higher orbit? Can this orbits be reached by a Shenzou spacecraft?

Greetings,

Daniel