I doubt single ranks would do any good.

1. Reason :
The enemy will deal damage to you ... when one o your men dies ... there is a gap in your formation and he might be able to split it ... using the triangle formation for example. Also Arrows would have an more severe impact upon your unit, since it will take more time to replace losses in the middle of your formation.

2. Reason :
Cavelerie will, no doubt, break your formation on the first moment of impact of their charge. They´ll just ride your men down.

Deep formations ensure a longer life ... while long formations give you the oportunity to "wrap around" the enemy flanks, delivering maximum damage.

Having the enemy break through your formation should have a vast impact upon your morale (routing), especialy when there are units to protect the flanks of the Unit achieving the breakthrough.