It you dont back off once the tiger tries to bully the double su76's it will most likely kill one su76. But if you back away your su76's you loose territory.
Having only a chance off 0,53% and 0,56% to pen the tiger at max and mid range it doesnt look good.
8x 140 damage or 9x 120 damage shots need to pen to kill it. When rng is 100% with you. Its about 15 or 17 shots when rng hates you.
While the tiger or a panther need only 3 to kill one su76.
a single su85 doesnt have much chance against a tiger or panther and it only needs 1 shot more to kill a su85. this is not a realistic scenario. you have to take in account army composition and where the units are placed . a single t34 a guards or a mine can swing the balance back into your favor