I took this picture in Buena Vista, Co to show the size difference between a Eurovan and a Sprinter before I bought my Sprinter.
For reference, that's a Eurovan "Full Camper" Winnebago conversion. With the rack on it it's probably right around 7' tall. My Westfalia Eurovan has a much sleeker Poptop and won't fit thought my 7' garage door with the Yakima rack on it.
The Sprinter obviously has a Poptop. You can see how tall the Poptop hardware is above the standard roof. But even without the Poptop the low roof Sprinter would be way too tall for any parking structures.
With the poptop it's probably only 6" shorter than a highroof? (And with this rack and solar probably the same height).
Just saying that once it's already too tall for parking structures the next upper limit it like 13'6" or something like that for low bridges, (my highroof is only 8'6" stock) so why not add the extra headroom inside?