Hi Tristan de Castelreng,
The wedge, or in R:TW at least, was best used, in my humble opinion, against tightly packed units that you deserately needed to break up! I always used it in the rear of almighty phalanxes to distrupt their formation and in the front of very weak spear-units. However, unfortuately, I lack M2:TW, so I cannot really advise you in that field. Sorry I can't help, good luck, cheers!