I have read:
"Flight of Eagles: a story of the American Kosciuszko Squadron in the Polish-Russian War 1919-1920" by Robert Karolevitz and Ross Fern
"The Diary of a P B O (poor bloody observer)" by Frank J Shrive (Archangel theatre)
"Gatchina Days" by Alexander Riaboff (flying for Reds, then Siberian Whites)
I recommend each of them for giving the flavour of their respective theatres.
I have tried many times to get the following, which is frequently recommended:
"Kosciuszko, We Are Here: American Pilots of the Kosciuszko Squadron in Defense of Poland, 1919-1921" by Janusz Cisek
Do not bother with:
"Last Train over Rostov Bridge" by Marian Aten
it is impossible to distinguish fiction from fact, and there is a lot of fiction.