Germany has to deny the NO SZ125 but Japan can deny it by taking out Amur.
Ran some numbers last night. If the USSR buys an additional fighter, with 4 bombers Germany still has a positive expected value from bombing G3. To make it negative, USSR needs to buy two fighters. USSR doesn’t want to spend money on fighters so I guess it is still worthwhile for Germany to threaten it. Could conceivably be worthwhile to attack even with a negative expected value because USSR’s money is worth more than Germany’s. The problem is that if you lose a bomber or two, do you have enough to hit it next turn?