Normally they face the front of the oncoming traffic, but that may not matter.
I got done by one which was on the other side of the dual carriageway and set up to get the oncoming cars. It got my across the barrier and so was able to get a shot of my no. plate.
I was also spotted (twice in one day, by the same van that had moved) while I was oncoming. The pictures show the front of my bike and the reg was written down by the bloke.
I got away with those two, though not through any specific tactic, just by wasting enough time that they didn't bother pushing them and just demanded that I tell them who was riding for the first one. All were in Wales.
P.S. if you get the NIP through, I'd suggest replying with the PACE reply. You'd have to be willing to take it all the way to court if they wanted to press it, but it's the best current loophole.
Here is a good place to start.