Kermit:
you will always have pilots (no matter what RP) who will only engage, when the "victim" is busy with npc's or the pilot has support from other players or npc's and those will mostly be "gone" when you could face again without them having any backup.
I personally call it being coward and they most likely call it strategy. But it is their choice to pick the way they want to face the opponent.
On the other hand, there will always be a point in time, when you can face them alone, without them having any support or backup.
I personally do attack my victims when they are "free" for it, but at some pilots I personally do not care a single moment, if they are busy or not. Depeding on my mood, on the experience I have with those pilots and on the npc's or opponents they are busy with.
There is no word, telling that a pirate has to wait for the opponent to be "free" to get taxed. Of course "waiting" is part of "fair play" (at least for my understanding). But then, life is not always fair.
And if someone has a problem with me engaging while being busy with npc's or other players. They are free to call for help and/or support, placing bounty, or when they feel unfairly treated, simply report me.
It's still a game after all
Happy missioning
ps: dont worry, I don't like doing RP in X since it mostly turns out being laggy. Sirius is bigger than X-3043 and if Sirius is not enough, then I simply go to Altair and/or Inner Core