I still haven't read the manual, so not attempted any to changes to the driving profile yet, but had another try of the ACC using
@roadtripper's advice re indicating once the "detected" warning flashes up. This certainly helped matters go noticeably more smoothly than my initial trial, so I was pleased with that.
I did, though, experience a couple of unnerving moments when the van started accelerating hard towards the vehicle in front (which it had previously detected and slowed down for), only to then decelerate hard a few moments later. This happened twice in quick succession, followed shortly after by a "sensor unavailable" (or similar) message, a triangular yellow warning light on the dash and the ACC disengaging. This all occurred whilst in a single lane contra-flow system that had metal barriers erected on both sides of the lane and 10 mins beyond the contra-flow, the warning light went out and ACC was available again.
Be interested to hear if anyone else had similar ACC issues and whether they occurred whilst driving through a contra-flow system.