Ok well the way I have it in my head goes like this.
Their TIE's arn't here yet.
So if I go attack the blockade inforcing ties NOW, at least some of the Convoy TIEs will peel off to come deal with me. And probably the Players as well.
That would leave an opening for the other guys to attack the convoy.
So I want to be attacking BEFORE the convoy breaks out of the forest.