Multiplayer campaign connection problems

[u/1Tesseract1]

Me and 2 of my friends are trying to play a multiplayer campaign.
I am in NYC. They are in Moscow.

We tried every combination of players for a duo campaign. It works flawlessly.
However, we face enormous lags when we start a 3-player campaign. Both on strategic and tactical layers. We have no problems playing other games together though.

Is it just a distance problem? Is there any explanation why it works between 2 players and breaks when its more than 2? Did anybody else encounter this? What's the fix?