This comment provides the jumping off point to talk more about dungeoncrawling in Old School Essentials and b/x-like games:

Not really a fan of this idea. Unless you are on a horse and trained in taking the Parthian shot. Especially if facing ias at all important in your game. Would you really want to keep turning your back on the enemy? And then turning back, reacquiring the enemy in your sight, reloading, drawing, and firing. And actually using a missile or thrown weapon requires a pretty solid stance (unless, as mentioned you are on horseback, which comes with it's own problems). Plus the fun fact that once you start running away from the enemy the tendency is to keep doing so,

My favourite definition of how rate of fire affects movement in a D&D game is from Swords & Spells, the OD&D miniatures rules, and which breaks down potential movement, firing, and reloading options according to fire rate. But on the strategic scale.

I'm also a fan of the idea that you can't use missile weapons in melee (without special abilities), and also the old Chainmail definition that you are in melee if you are within 30' of an opponent. A melee in the historical sense of the term, rather than merely being actively engaged with an opponent with melee [hand-to-hand] weapons. Thrown weapons can be used whilst entering melee, of course. I do like zone based combat. It works well, especially in a swashbuckling game.

The use of miniatures has tended to encourage the idea that combat is very static; that the combatants stay where their miniatures are placed, but if you actually look at two engaged individuals, especially ones trained to fight on foot, they are in continual movement. Which is why cavalry tend to fight poorly on foot). "D&D, with a combat system originally based on a mass battle scale wargame has always been quite poor when it comes to handling skirmish level combats. I do recommend something like The Fantasy Trip or Ironclaw instead (my personal favourites). [Although Eldritch Wizardry did try to fix this by introducing segments (which nobody really used because nobody wants to move their figures one hex at a time.] The division between melee, missile and movement pretty much assumes you are heading into engaging in melee. This really does smack of rules lawyering to me...