Great thread!was correct when they suggested moving to the hub center method. Tire profile and pressure always cloud the rim-to-arch reading, so it's worth comparing your new numbers instead.
Your comfort to sport drop appears to be about correct for these vehicles, if that helps. In Sport, Airmatic lowers the front end by around 20 mm and the rear end by about 10 mm on the X218; these dimensions correspond to your 670 to 650 and 640 to 630 measurements, respectively. Therefore, nothing there shouts that something is amiss.
What would actually reassure me is that the two sides read the same, 670/670 and 640/640. When the level sensors show that the airmatic is at the desired height, the struts and accumulator are evenly holding the pressure, which is why symmetric readings are important. A worn strut or a leaking accumulator would have caused one corner to sit 15 or 20 mm lower than the other. Put your worries about it drooping to rest; it appears to be level on yours.
A few things to keep in mind so that other people's measurements are fair. No one else in the car, same tyre pressures, about the same amount of gas and on a flat, level surface. The readings obtained after a run and those taken after parking for some time might be slightly different because Airmatic adjusts the ride height depending on the vehicle's position.
Even with the steel front, Cherrypd, your husband's rear air figure will serve as a good stand-in for the OP's Comfort rear, as both rears will self-level to their respective targets. True to what the OP stated, fronts will clash.