When you talk about "grade," I am assuming you are talking about the superelevation of the roadway, which is the lateral grade of the roadway. I wouldn't expect the "grade" to make a difference in contact height if the "grade" is constant across the travel lanes, as the contact points on the two vehicles would be essentially occupying the same lateral position on the roadway at the moment of contact.
You might, however, consider the lateral acceleration being experienced by the vehicles at the moment of impact. If both vehicles are traveling around a left-hand curve, then both would be experiencing a weight shift onto their right-side tires/suspension. If both vehicles experience about 1" of lateral weight shift as they travel around the curve, the contact points would be about 2" higher on the vehicle in the left lane and about 2" lower on the vehicle in the right lane.