I wait in Posta di Vera Croce (True Cross Guard) because you are too close to me. My right foot which is in front, I will turn behind me, and I will beat your spear offline to the right. My thrust will not fail, but yours will.
Posta di vera croce is a rear weighted stance. The bulk of your weight rests on your left foot, with your knee bent. Your right leg is straight, stretching out toward your opponent. Raise your heel slightly. Such weight distribution allows you to occupy a given space, but move your body further away from your opponent. Your hips are well chambered. You right foot can easily slide to a new position without your body moving, giving this a degree of deception.
Each of your hands rests by its respective hip, with the spear aligning along your belt. This ties it directly to your hips and core. The butt of the spear points at your opponent, and you look over your shoulder at them, as shown. You are providing an invitation to your opponent. Your face and whole right side are apparently open.
The text tells us that this is a good posta for if your opponent is closing in. The rear weighting of the stance, the mobility of the front foot, and the fact that the spear butt does not extend so far, all combine to give you a bit more room to move.
As your opponent moves in to the attack, slide your right foot across so that your feet are shoulder width apart. Also slide it back to give yourself appropriate distancing. Fiore tells us you can step back well behind your left foot.
The line of your spear extends the movement of your hips, and the direct connection to your core gives this move a lot of power. You can either catch the incoming attack with the tail of the spear below your right hand, or catch it between the hands. The master play of the sword in armour demonstrates this second method. When doing this, keep one hand tied to its hip and move the other as little as possible. There is no need to push the attack out to the side. It is a deflection. If the attack misses by an inch, then it has missed and you are safe.
Drop your weight forward slightly onto your left foot, which will now be in front. This is not a big lunge, but a small drop to add weight to your counterattack. Drive your spear into your opponent.
Other examples of posta vdi vera crose can also be seen in the following.