>Estimate seems low
Yes, but that's the maths. It does suggest the ride height of the person taking the photo is higher.
The main point I'm making from the estimate (apart from an estimate about the height - which can GREATLY vary according to small issues, which you'd know if you've done this kind of stuff before - which is also why I tried to calculate a range) is… perspective is taken care of automatically when you use the horizon in the calculation.