16 we used last year was shorter than the Scamp
and there was a tendency to bang one's head all over the place. As a solution Ginny hung a single piece of red yarn from key spots, the outside door, the vent handle and the bathroom doorway.
Though I never consciously see the yarn it seems to provide some kind of subconscious warning.
I will agree that the Casita's doorway seems to be a lot more head prone than the Scamp's. I think, though can not verify today, that the Scamp's door is cut further back into the floor, encouraging one to step down more quickly in the process avoiding the top of the doorway.