These wards have a rigid attitude towards their relationship to the line. They either have to be on the line, or off the line, and they don't change their minds about this.
Poste's Breve, Dente di Cenghiaro, Porta di Ferro Mezana and Dente di Cenghiaro all need to have their points on the line. They're at a disadvantage if they're off the line, even the slightest degree.
Coda Longa, on the other hand wants to keep it's point off the line. This gives it maximum time to react, and get the blade in play. It keeps the blade length hidden. It maximizes the distance from the opponent. In addition the fastest way to get it moving is to simply push down on the pommel, while throwing the quillons forward, if it's off line, this will cause the attack to be off line. Coda Longa has the same attitude towards the line, it's just in the opposite direction.