Game mechanics question: firing in stacks?

[DaveK]

I think I've asked this question at some point over the last decade, but I forgot the answer: is there any mathematical difference between firing separately versus firing in stacks?

For instance, say I have three units with 10-tanks each facing an enemy unit with 1 tank. Are my chances of inflicting damage on the enemy unit modified by selecting each of my three units individually then firing versus selecting all three of my units and firing as a stack?

I ask for the simple reason that if all things are equally, I'd rather stack fire simply to speed up the game. But if it's costing me something to do so, than I'd rather not.

(Same question applies to the modified fire rules permitting damage against entire stacks... again, does it matter if I fire each of my units individually at an enemy stack versus firing my units as a stack against the enemy stack?).

Thanks for any technical answers...