Moscow

Beijing

Here is a nice simple example - because the journey is non-stop,  ALL the kilometers are classed "International", so priced as the subsidised rate - making this the best-value kind of trip, except that you can't stop.

Moscow

Ulaanbaatar

Beijing

This is quite good too - Ulaanbaatar (Mongolia) is an international destination from Moscow, so the km's from Moscow to Ulaanbaatar are subsidised-price.  The km's from Ulaanbaatar to Beijing are not (because they have no agreement on that route) - but this is still good value.

Moscow

Irkutsk

Beijing

Here's where things get complicated.  Moscow-Irkutsk is a domestic trip,  so the km's cost  a lot more.  You get the International Subsidy, but only from Irkutsk onwards, where you are "Int'l".
The more stops you make, the more the Rail Tickets will cost.  Any Trans-Sib trip is a compromise between the lower costs of not stopping,  and the excitement of the things to see en-route!

(NB these are not OUR rules - this is how Russian Railways price things,  and the same will apply whether you book your trip with us,  or elsewhere.  We just tell you the truth,  mainly because we actually know what the situation is!)