Translation
I am positioned in Mezza Porta di Ferro (Middle Iron Gate) with the spear. Beating and wounding is always my custom. Come whoever wants. With a short spear or staff, the beat with a step will not fail to wound, and all guards which step off line with short spear and short sword are enough when facing any long hand held weapon. And those which cover from the right, cover with a pass and a thrust. And the guards on the left side cover, beat and injure with a strike but cannot thrust well.
Explanation
In the description of the Spear Posta Tutta Porta di Ferro, Fiore makes it very clear that the spear postas are just sword postas used in a different context. This is interesting in Posta Mezza Porta di Ferro, because when this posta is used with a sword, the right foot is forward and the point is on the centerline. By leading with the left foot here, the spear point has to swing off to the right. Functionally, this stance more closely resembles Sword Posta Tutta Porta di Ferro.
Regardless of nomenclature, all Fiore spear posta hold the point offline. As he points out here, all his spears and any relatively short weapon all make the same initial defence.
Slide your front foot off to the side. Beat the opposing spear point to the side while passing your back foot to the front. You will now be able to deliver a counter thrust of your own.