I think the whole convoy/plunder system should be changed for the simple reason that group strength/rank/level do not matter anything in it even if is a group activity. Imho convoyer should be supported on auto by two weaker than him people in his group or by one stronger person that accepts to support (so should be a 3vs1 battle with two autos or a 2vs1 battle with manual playing) and that the stats of both the attacker and the defender should be increased by a certain quantity that depends on the group rank (like the stats of the summon snake). This way would be fair.