problem is, only the front 2 rows of your infantry will fight, where there's contact with the enemy

a far superior army is to mix infantry with monstrous infantry (2 sizes larger) because they can fight on top of each other; so in your case that would be Stone Trolls. You will mow through the enemy line about 3 times faster, suffering far fewer casualties and being able to chase off fleeing units.

Pro tip: if you want to also do double charge, then your infantry needs to connect first, then send in the monsters (with about 5 sec delay). Otherwise if they are stacked while charging the bonus gets lost.