How to use scythed chariots?

[Morte66]

From what I've heard, you should order them to move behind the enemy (with guard mode on), so that they just go through the target, ripping apart the formation. Then quickly follow with heavy infantry or cavalry.

I think I read something like that, but it's very imprecise. Can anybody say what "move behind" means in this context?

Does it mean move from the front of the enemy to the back, passing through the enemy formation?

Or does it mean move from behind their left to behind their right, just catching their knee tendons with the scythes?

{edit} too slow, Pharnakes got there.