Chas,
The highway itself wasn't sunken, the sunken road ran parallel to the highway about 200 meters away.
According to the account in Daniel Taylor's book "Villers Bocage Through the Lens" Wittmann broke cover on the south side of the highway and came across the rearmost elements of A Squadron, some of which had begun to disperse into the field south of the main road for defensive purposes. "These he briefly engaged before turning left onto the road towards the town" Once on the road he began firing on the halftracks of A Company which had been parked along the righthand side of the road. I think you would be Ok putting a Cromwell from A Squadron on the road, but when looking at the maps and diagrams in Taylor's book it doesn't appear as if the rear of A squadron was close enough to A Company to put them both in a dio, but you could use a little artistic license here I guess.
If you can get your hands on a copy, Taylor's book is very good. It gives you maps, diagrams, good pics, and a blow by blow account of the battle. It is generally regarded as the best account of the battle. To top it off, it's not that expensive, 25-30.00 USD.
Cheers,
Mike