Learning Fiore De Liberi

Posta are body positions. They provide a convenient way to talk about options and things to do. In general you should move from a posta, through a posta and to posta. If you're attacking, then you will almost always cut through Posta Longa. If you're covering (ie defending), then you're most likely going through Posta Frontale. However, you could also find yourself going through Posta Breve just as easily.

These wards are attitudinally ambiguous with regard to the line. You can hold (not referring to how you grip the sword) them rigid or loose with regard to the line.
Both di Dona for instance have an alternate form where the blade is pointing right down the line. Porta di Fero can be done with the blade anywhere in the front right between 12:30 and 3:00. The blade, in terms of where it is on the line, is fluid. It can be held on the line. It can be off the line.