These are the basic rules of dueling as i know them.
Set merge altitude. If it's 3k, then you can not go above that altitude until after the first merge.
Once in icon range you can dive as low as you want for speed.
The first merge is guns cold.
After the first merge, all rules are gone.
I used to not take the "ho" or deflection shot on the 2nd merge, but lost many duels because of it, so now i do. Seemed like every time i would hold fire, i'd end up with a pilot wound, or smoked engine, or lost wing, because my opponent didn't hesitate to take the shot.