A war engine may barge if it is counter charging.
I take that units that are in b2b or come into b2b contact with the WE are no longer considered to be the nearest units for the purposes of working out the direction in which the WE must go in. Ya?

Reading the rules I'd say yes, as long as it has no more than 2 x its DC on it before or after the counter charge, and once it gets to 2 x DC it would have to stop.

i would reguard it as ZoC - so contact one lose it, but if in ZoC of another procede towards it etc.

Yes a unit in b2b loses it's ZOC

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Yep. The "must charge unit X" is based on Zone of Control which, as everyone has pointed out, is lost on contact.

Still, in practical terms, it's hard to not have to barge up in the middle of the formation once you start. The chain of overlapping ZoCs is hard to break.

well it's not that I was worried about lol - i was thinking about counter charging towards any enemy potentially a huge distance away - but for what purpose I won't reveal

Ah. You're still restricted by "must countercharge towards the closest enemy", so to do that, you'd have to have all the closer units in base contact. Seems unlikely, but if it happens, then you could keep going towards the next closest formation.

happens all the time!

Don't forget that the countercharge is a very restricted distance. In the case of most titans and Orc WE transport this is a mere 5cm, or the ZOC of one unit. Scout titans will be able to get 10cm countercharge.
The best you can do is some form of fast transport (eg Rhino) to countercharge and then dismount for 15cm total. Either way, this is not going to be 'huge' distances IMHO.

As an additional note, if troops do dismount from a countercharging transport, do they still have to move towards the nearest enemy as technically the dismount is not a coutercharge, so not subject to the countercharge constraints?

that's ok. I wasn't actually interested in actually making it into btb contact with another formation. And yeah, 10cm is better than 5 for what I wanted it for,

On your dismount note: I think most would agree that they do have to move towards the nearest enemy.

Dismounting is part of a move, so it would follow all the same restrictions.