I am watching "The Patriot" so my history is already muddled there but in the battle scenes, both sides always line up in single file and fire a volley. I get why they would do that (flintlocks were not modern rifles) but my whole thinking was, since each side essentially tells you when they're going to fire, why not just drop to the ground?
Apart from the possibility of hitting someone behind you, the shots would sail overhead.
Was it part of the gentleman quality that combat had at the time?
It's not about 'gentlemanliness'. Formation fighting has, until the advent of smokeless powder, been the way to fight. I commend to your attention the appropriate section of the FAQ on Early Modern Warfare; you want everything under a heading that says 'linear tactics'. I recommend starting with u/tyn_peddler's answer here, and moving onto the rest.