You can surround just a single non flying model... remember after the charge phase (2d6) you get 3" pile in, swing, then 3" consolidation...
You can go anywhere a base fits and just stay like 1/4 away then swing around behind a model base to base... you just have to end both of those 3" moves closer to the enemy not directly towards by the most direct route. Use that assault speed to penetrate the enemy lines and trap them in that shooting protection known as ongoing combat while ensuring you can't be counter trapped to fall back and charge... it will be your advanced level play.