This post has flown in so many directions. The big boys can be there as long as they do not attack the trader. There is nothing about not doing anything in the rule. If they are running a screen for other big ships, they are not pirating. There also should be absolutely no reason for the pirate cap to fire at the trader. Yeah you can say self defense, but outside a Luxury Liner and a Contrans, how many traders can hurt a Cruiser, realistically?
As for the RP aspect of pirating, there is a failure on both sides. It is such a fast interaction till the trader is stopped that there is little room for it. I like getting the demand out of the way with "stop or die" because it is fast and dirty allowing you to weed out the RP'er and the cannon fodder. After that, the RP can happen.
I really do hate the traders who expect a service. We pirates are not here to be polite or to defend you. We are here to rob you, or kill you if you do not pay. Anyone Pirated by Basilisk has seen this theory in action.
The original purpose of this post was to look at a grey area that everyone demands is "black and white." It is not. If it was, we would not be having this thread. (A question that was answered BTW)
In the end I think we have to look at why these rules are here, to keep all of this fun. We cannot use a cruiser to pirate because it would basically be bullying. Not fun. It does, however, add to the experience to have that cap visible obviously waiting for some lawful friends to show up.
Ever think of how it would be to pirate in a dessi? How much of a chance do you think you have against a swarm of hungry lawfuls just salivating over the explosion your ship is about to make. I personally love the ability of a smaller ship to get the hell out dodge. That will keep you alive far longer than your 12 turrets.
That's my rant take it how you will. Just remember to have fun and keep it fun for the other players. I think that common sense, a good grasp of the rules and sportsmanship will keep you out of trouble in the long run.