There's a whole science that is solely concerned with surfaces - between water and air for instance, or solid objects and the space around them. There also happens to be a bunch of really interesting mathematics associated with these surfaces, with limits, and the edges of things but that's not important.
In dueling, the most interesting and important edge to understand is the edge between safety and threat, and how this changes over time. This edge appears in the space in which you are playing, and is also related to the geometry and design of the sword you are carrying .... Because safety is not just about being out of range, but can also be anywhere off the cut line of the weapon.
I had the pleasure of playing a little with German long swords recently with a couple of friends from Valkyrie WMAA. It was just a mere dabble, but what came home to me from the few techniques we played with was how different the geometry of 'safety' is, just by adding a sturdy cross piece in front of the hilt of the weapon.
I am used to fighting with no hand guard, mostly because my art comes from a culture where daily carry blades used for work did not have them. Hand protection is much more common on weapons designed specifically for fighting because opponents often target the hand, but machetes, Goloks, Bolos etc generally do not have hand guards, because sugar cane, undergrowth, and coconuts, do not.
It's a whole new world out there with this one, small, added piece of steel. A parry or block that using a Pinuti would take your head off, is now safe (relatively), and traps and redirects take on a whole different meaning.
Any sword you use should become part of you, and through that, so should the experience of the space you 'own'. This takes time, work, and familiarity, and if you don't play enough near the edge, you'll never truly understand it's limits.
I would love to get to the stage where the mere feel of a certain sword in my hand would translate into the geometry of space, but because of the sheer variety of swords designs in the world, that sadly seems unattainable. Even getting to grips with the swords of the Philippines would be a lifetime of work.
However, this does not mean one cannot infer usage from design, and learn from different designs about the space you move in and the changing options each gives.
Sonny thought of every weapon as a tool that taught you something specific, and when we flowed we went form one to another to see how the concepts and attributes crossed over .. or did not.
The better you get at understanding this of course, the greater your movement options become, or the perhaps better said, the finer your angles get to become ... and in sword fighting that can mean the difference between a graze and being run through.