If you face Corran Horn w/ any fat turret….kill Corn Hole first. Trap him and go after him. Double stress him if you can or just pour as much fire on him as possible. 3 green dice is nice, but fickle.
If you face a Phantom….kill that first. The 4 red dice are no joke and you should try to trap it and kill it ASAP or it will eat your list for lunch while you chase the Decimator.
Kill the escorts first versus the turret is always going to be a debate, but yeah - when you've got something like corran, try to kill him dead - anything with regenerating health needs to stay down, and if he's packing R2-D2, he's not got a generic R2 astromech - which means he's probably nailed to the green manouvres, so he's actually more predictable than the pancake.
If it's a pack of TIE bombers or Z-95s - something with lots of toughness for its cost - then don't try and fight them first.
I think one of the strategies which might get some success is knocking down the escorts and then running away from the fat turret.
If you can manage this and minimize losses to keep your points advantage, getting approximately 40 points of kills down (say the price of 3 Z95s, Soontir, or Corran for example), running away for a while might be a decent strategy. Not going to say I think its the most honorable one, but nothings fair in war.
Its hard because fat turrets are often very fast with boost and can close the gap, but if the turret is hugging the outside of the board they are going to have limited maneuver options and may not want to come through the rocks to get you. If they do, you might be able to get a couple of turns of blocking/jousting in which may decide the game. On the other hand if you want to maintain your distance, small ships can go the opposite way around the outside to maximize the distance between the fat turret and them and also cut through the rocks to stay out of range. Would be frustrating for the fat turret player, but its nothing they havent done to all the real fighter pilots