How does FF work in ETW?

Let's say you have 2 units, each 3 ranks deep, one behind the other, like this...

1111111111111
2222222222222
3333333333333


4444444444444
5555555555555
6666666666666

If they're on level ground, will Rank #4 shoot Rank #3 in the back? I have seen this happen, but seems maybe 2-3 FF kills per volley. Nothing like the pilum-in-the-back FF from RTW.

Without Fire by Rank or any of those other cool technologies, will any ranks besides 1 and 4 fire?