How can I get PD to target seekers, not fighters? I'm dying out here! :(

My PD often targets fighters, thereby letting seekers through, which destroy my fleets. I've tried correcting this by going into the tactics screen (the crown icon) and editing the "maximum range" tactic to select "target type" first, and have "seekers targeting me" as the first item in the list. No dice. My PD still targets fighters, not seekers. Any advice would be greatly appreciated. (In fact, if some kind soul could explain the targeting system to me, that would be really helpful. It often does not do what I expect. I was under the impression that if I chose "target type" as my first priority, my ships would target the items in that list from top to bottom. Evidently not). Thanks! DB