To update:
I just flew with the bag on Air Baltic which has a 55x40x20cm size. This is the same size as Ryanair and Aeroflot uses. Even though this bag states its 22cm it fits just fine in the Ryanair, Aeroflot, and Air Baltic sizers. Just make sure its not overstuffed (with 8kg limit I dont think thats a issue).
And it fits in the overhead Air Baltic DH4 and Eurolot DH4 planes.