OK, so I looked a little further into the utility of 50* mortars.
I am going to assume that only crits are useful, which is unfair to the mortars, as 2/+2 shots against units in roofless buildings will do stuff, but the math is much easier if I don't think about them.
A single mortar needs to make 36 TH rolls in order to get a critical hit. Let's use
@witchbottles nifty trick of not taking ACQ (we can definitely do that), and also assume that we can put a +2 hindrance of smoke or debris between us and the target half the time (not sure how practicable this is). That means we only need to make 15 IFT rolls (all useless except the one). That's 51 rolls, or the following number of SAN activations:
SAN 2 = 0.5
SAN 3 = 0.9
SAN 4 = 1.4
SAN 5 = 1.9
SAN 6 = 2.4
SAN 7 = 2.8
Imagine mortars are the German's best weapon (at least, among those vulnerable to snipers). If that's the case, then the Russian's interest might be to dedicate his sniper to incapacitating their crews, i.e., using "2"'s to position the sniper where it is most likely to break or kill a mortar crew on a "1". At what SAN does the Russian win, i.e., is it likely that the sniper gets the crew before it lands its critical hit?
A lot of that depends on where the mortars are in the battlefield, of course. If you were able to put them up in the front lines surrounded by other units, then they might be effective no matter what. If you have them by themselves perched in a rear area, then my guess is that a SAN of 6 or 7 is enough for the Russians to win, but a 5 or less gives the Germans the upper hand.
Of course, that assumes that mortars are the German's best weapon. If something else is, then the Russian should ignore the mortars and use all those SANs to let him hunt whatever that thing is. He'll probably hit a 10-3 led death star less often than he would hit a mortar team, because the death star is more easy to surround with other units to distract the sniper, and the MMC he's leading will take some bullets for him. But on the other hand, a "2" sniper against a 10-3 is just as good as a "1" 50-67% of the time, and does you a heap of good even when it doesn't kill him outright.
So the question is, how many cracks at my death star are I comfortable giving the Russian sniper in order to get that critical hit with my mortar? I'm inclined to say somewhere in the 0.5-1.0 range. 1.5 (= 4 SAN) might even be doable if I thought the terrain was favorable (i.e., a lot of debris hexes to put sacrificial lamb halfsquads are near where my death star will be). This is higher than I originally thought, but not by a ton.