I’ve found out that I cannot set articulations via the default shortcuts in a Portuguese keyboard layout on the iPad. However, I’ve found out a way to work around it.
These commands are assigned to the character on the top of the number keys, which is actionated by pressing the Shift key. This works on the Mac, but not on the iPad. But, if I reassign those commands with, say, Shift+1 which, in a Portuguese layout, produces “Shift+!”, it works.