Yes the damage done in retreat is a major component of the losses you see if you don't watch the battle. It was why I always felt the 2:1 rule for the russian's was acceptable. The russian's suffer extreme losses in a battle during the fight itself, if they fail to win it can be murderous.
Mortars are the biggest killers in the game. 120 mm mortars will fire 3 times, 82 mm mortars will fire 2 times and 50 mm mortars fire once in terms of range. Once the russians start getting large numbers of heavy mortars into their formations losses for the axis mount significantly. Also the mortars have a high rate of fire so the fire at long, medium, and short range by the 120 mm mortars will inflict a lot of damage. The substantial change in combat losses you see starting in early 42 is almost assuredly due to the 120 mm mortars showing up in large numbers with the TO&E changes to russian infantry divisions. The SMG squads only add to this...
How much fire you get from a unit is strongly dependent on the units experience. High experience units will inflict significantly more damage than low experience units. If units that could fire in mid range combat do fire (or fire effectively) is a factor of experience. Units will low experience rarely fire rifles, MGs or SMGs in mid range combat. High experience units put down a signficant amount of fire there. Another reason for higher losses starting in 42, the russian units in 41 will almost never fire small arms in the mid range combat (making hasty attacks much less painful for the germans).
AT with experienced crews do well. They equally often seem to fire on everything but AFVs (russian 45 mm AT guns in particular). Anti-tank rifles seem to be far more effective in the game then I've ever heard of them being in real life.
Artillery in the pre-bombardment phase seems to have a large effect (even it it doesn't do much damage), as the biggest difference between a hasty attack and deliberate one is that a hasty attack forgoes the initial artillery duel by the attacker, and reduces fairly significantly their mid range combat. This seems to increase the losses to the attacker due to the lack of suppression.
It should be noted that fortifed zones and regions have a huge impact on combat, artillery fires more often, and fires more accurately. Early war as the russians this can dramatically change your combat results...you may loose but the damage you inflict on the attacker goes up by a significant amount.
Winning and loosing battles for the most part comes down to men, tubes and tanks. CV isn't an issue in the combat itself which seems to be resolved "operationally" or "tactically." Also so far as I can see there is a morale check of some kind in combat. Units will hold, in general, until the attacker inflicts 10% of their starting numbers in casualties at that point the defender will usually bug out. How many casualties you have to inflict to force them out seems to be dependent on the initial morale of the defender, I've almost never seen a defender hold past 20% or once hits on support squads start showing up. But I have seen a unit withdraw the first time it was fired on by a rifle (it was in bad shape). This may be an automatic odds calculation thing as well I don't really know. It just looks like a morale check failure. Defending units are not fired upon by every attacking unit and then odds are calculated unless they hold. If they withdraw/shatter/route/surrender the combat can be terminated before all attacking units have fired. But a unit will stay in place until the short range combat starts.
The post combat retreat is what drives losses that you see in low display value combat results. Attacking a german security Rgt early war with 1 Cav, 1 Tank and 2 Rifle divisions cost me six times the losses I inflicted on the germans in combat, I ended up with equal losses due to the combat losses inflcted in the retreat. My current rule of thumb for a successful russian attack is to have 5x as many men/tubes/tanks as the German. The only thing I use CV for is to tell me how strong the enemy is compared to a full strength unit of that type. When playing the German this is problematic as 1 can mean a great many things, but for the russian the units CV is proportional to their TO&E value.