The issue you're having is that the Door you see is for an internal staircase of the building (you can see the scaffolding for it in the second picture), which is to the left of the incline (from the first picture's perspective). The orange line you drew representing the wall of the building needs to be shifted further right in this first picture to line up with what you're measuring in the second picture. That shortens the distance of the drop you measured.
Edit: To explain the optical illusion, the incline happens behind the door/staircase, you drew it as if it was in front of it. If that makes any sense.