What i do (i am one of the top5 in my merged server) is to run S convoys only where there is the food trial in rich field and to plunder when there is the coins trial.
What praiseluka says is true and there is also to consider the fact plundering is one of the main activity that drives away players from this game.
In a new patch of the game the convoy/plunder system gets modified so it won't be anymore as is now, but the current system is too appealing for strong players if your server is not a dead server.
What i honestly think is that the system should be reversed, in the sense that top20 people should not be able to plunder, but only 21-50th place should be and that, at most, top20 should be given a chance to support weaker players plundering attempts for a 25% of the eventual reward up to 3 times per day. This way the things woud work out way better.