I adopted the horseshoe formation for defending bridges way back in the STW 1 days. Once muskets became available, it was the best way, IMHO, to defend against a multiple stack attack. When battles take 1 1/2 hours to 2 hours (real time), and all day (game time), you have to keep your troops as fresh as possible to avoid routing.

In RTW, I will often arrange my forces in two groups at nearly 90 degrees to the river, and place my general with a few of my best infantry in the middle facing the enemy. If the troops crossing turn to attack one group, they get it in the flank from the other, and vice-versa. If they go for the general, they get it in the flanks from both sides.

Personally, I think they should have allowed for crossings at shallows along the river at several points. Would be more realistic, and make things far more interesting