All distance is dictated by ma-ai. The 'timing'-distance-interval it takes to initiate a waza. It has nothing little to do with how far away someone is. If you look at classical arts one of the main differences you will see is an exponent creating his own ma-ai to deal with anyone that enters inside it. Whereas you could perhaps describe more modern arts as two spotlights dancing around on a stage. The only relationship to the feet is what is described as a one step cutting distance. If someone encroaches inside your ma-ai they are technically 'dead'. You can again alter that ma ai for safety reasons but that is considered dishonest. You should "deal with it". The OPs original post mentions footwork in relation to swords. The subtle difference is that ma-ai is extended to the kensen of a weapon you wield as part of your body. That again depends on the length of that weapon. I prefer not to relate any of these arts to "modern times". A few weeks ago someone threw a grenade at my friends car (retired marine). Didn't go off so they drew silenced pistols and shot him. Riding in tandem shooters will do this for around 200USD.