Glamouring a wand over a staff

[Rongway]

You're not, not sure why to be honest. You can glamour 1-slot items over 2-slot ones in other circumstances.

It's probably a type restriction. Let's say you want to glamour a tunic over a cloak that forbids headgear. The two are both of type "body". One-handed and two-handed weapons, however, are two different item types.