This pairing is interesting because of what Fiore says about di Fenestra: "And of covering and of wounding it is Master", while of Porta di Fero he says "This is also an excellent ward for exchanging the thrust, and thrusting yourself.". So the obvious thrust that di Findestra has will not work against Porta di Fero. Porta di Fero will easily be able to exchange the point or break the thrust.
This particular pairing pits a ward suited for thrusting, against a ward suited for breaking the thrust. Posta di Dona Senestra can also make excellent Fendente's, but takes a longer tempo to get the blade around to attack, in this long tempo Finestra can thrust. However, with the blade cranked around the back of the head, di Dona Senestra is also nicely suited to deliver it's own thrust should Finestra takes it's point off line to deliver it's own fendente, mezzana or sottani. In their response to any cut, both wards do the same thing, deliver a thrust before the cut can materialize.