"Culo casto" is definitely a posibility. And an interesting one.
In this case the different heights of the letters might be for esthetic reasons.
Regarding your classification for rapiers, it matches pretty much mine. As I said earlier: "the rapier is defined by both the blade and the hilt." An yes, the presence of a functional ricasso able to be used for the finger is quite essential for defining a rapier (hence the "rapier grip"). However, this is much more important when distinguishing the early rapiers from the side-swords. But I think such a discussion is worth a new separate thread.