Yeah, there are a few key components at play here:
-Must be a line, which means you can't just snake around totally crazily in terms of the general path, but the line can go to any point of the enemy unit.
-Said line has to have 2.5" clearance, but that clearance doesn't need to be centered on the line.
-At the end of the thing, you need to end up able to place your unit such that it can get half or more of the engaging side lined up with the enemy it final rushed without any illegal overlap.
I think that's about it.
That is about the clearest I've seen it explained and I highly commend that UvulaBob put it in the rules to that effect.
BTW UvB I have recently found access to a binding machine, so I'm ready to print up those rules as soon as you say they are god to go. You're so flippin' awesome for doing this!!!