Carrying the sword like this is called posta coda longa and it is very good against lance and any hand held weapon when riding on the right side of the enemy. It is well to bear in mind that the thrusts and reverse blows are beaten outwards, that is, across and not upwards. And diagonal blows are likewise beaten to the outside, raising the enemies sword a little. You can do the plays as drawn.
Both the 7th and 8th master of horse are the same. They are drawn as two separate characters to demonstrate the applicability of this posta in a variety of contexts. Where the 8th master covers against roverso blows, the 7th master shows the use of this posta against mandritto cuts as well as thrusts.
Ride in a long straight line at speed toward your opponent with your right arm crossing the body and the blade trailing behind you in posta coda longa. Due to being mounted, it is not possible to put any hip action into your beat. It is instead driven by a sharp contraction of the shoulder blades and expansion of the chest. The majority of the force, of course, comes from the movement of the horse. You are really just giving direction to the sharp end of it.
Fiores point that you beat your opponents weapon across and not up is an important one. Whereas on foot, you would cut up on a clean diagonal line, doing so here would cause you to strike your own horse in the head. Your sword needs to move in an arc up the side of the horses head and then across over the top of it. This lateral movement also serves to ensure that your opponents weapon is beaten well off line. It is by clearing your opponents weapon like this that allows you to move on to the plays of the 8th master.