If I have only 3 armor and fighters left and Germany has a fighter only, I’ll retreat. Why? Because that’s 15 IPCs worth of units I don’t have to rebuy and they can add even more defense to Caucasus.
If Germany has an Armor and Fighter, I’ll press the attack. Cost is the same on both sides.
Financially it breaks down like this:
Russia attacks with 3 Inf, 1 Art, 3 Arm, 2 Fig vs Germany with 3 Inf, 1 Art, 1 Arm, 1 Fig
If you are at: 3 Arm, 2 Fig vs 1 Arm, 1 Fig the
Cost so far is: 13 IPC vs 13 IPC
Punch is: 15 vs 7 (AKA almost guarenteed to get 2 more hits next round and receive 1 hit in return.)
That means you cost Germany 28 IPC, gained 3 IPC for the land, lost 18 IPC for the attack.
Germany retakes, you kill probably 1 infantry, maybe 2 on the retake. So you loose the land bonus, but have changed the ratio to 28 IPCs in units lost for 31 IPCs in units killed.
Now, if Germany was reduced to just a fighter you can leave all 3 tanks there (15 IPCs) to be slaughtered netting you 1 or 2 infantry (3-6 IPCs) in casualties, or give him the fighter (10 IPC, less then 15!) and have a much larger stack in Caucasus to hit Ukraine later.
As I see it, Russia is perfectly capable of putting 15 Infantry, 1 Artillery, 7 Armor in Ukraine on Russia 2 with a retreat. Odds are that means you own Ukraine for a couple of rounds, until you are forced to retreat or Germany’s dead in the water due to allied actions.