I like data as much as the next guy, but I'm gonna come out and just say it: there's absolutely no way that at a -14% range hit is representative of the energy consumption penalty with a roof-top cargo box. I had a 11 cu-ft Thule cargo box (which has a smaller cross-sectional area as yours) that I road tripped with a handful of times with my model 3 2018 RWD and only on my best days would I get around 300 Wh/mi, especially at fast highway speeds. I can't recall the consumption exactly, but I remember my roadtrip from SF to SD (1,000 mi) and back probably averaged somewhere between 375-400 Wh/mi. We were fully loaded with 5 people and their stuff. It was in September, so wind resistance was at its most kind. I remember the efficiency was absolutely terrible because everyone in the car became miserable by the end of the trip. We stopped so often for charging, and it didn't help that some charging stops lack real amenities. If you have any significant headwinds with a rooftop cargo box, the efficiency drops sooo much.