According to Wikipedia (risky source on things Polish, but for the purpose of the thread...), the USSR was offering far greater concessions than Poland took at the end of the Polish-Soviet War. This was because the National Democrats under Roman Dmowski did not want more non-Poles in the country.
What if Pilsudski's views triumphed over the Endeks at the negotiations, and Poland came away with much more at the end of the war? These are the main points:
Minsk is handed over to Poland, presumably to be the root of a Belarussian satellite state.
The independence of the Ukrainian People's Republic is assured.