Tarkin Nuke

It's rng then. if lucky you do 2-3 hits evenly dispersed on all the remaining enemies. if unlucky, all the 12 hits go to the lowest hp enemy...
But that's the chance of winning a lottery!

Plus, try this: put the playspeed to 1x before using tie attack, and see how much damage each hit does. Mine did 10k for non crit and 15k for crit a few days ago. It helped me to expect the outcome more accurately at least. In my fleet arena enemies usually have 50k~100k hp+prot, so tanky ships with almost full hp protection are very likely to survive

It pretty random I also had all 12 going against one ship with only two ships remaining on the opposing side (needless to say all 12 hit the almost dead ship)