I would concur that flashguards were not around then. A couple of thoughts on how it was done 'back then'...and why we seem to need these silly modern flashguards to keep our faces from getting scorched off.
One of the issues is over-priming. I think as a rule, most of the reenacting soldiers today put too much powder in the pan.
Another aspect to consider is discipline. With the endless routine of drill...drill....and drill these guys went through, they became very good at the loading and firing routine.
In checking the Von Stuben and Smyth drill manuals, (Rev War through 1812) the maintenance of the line and proper placement of the feet should address most of the problems of getting flashed. If done by the book, the flash should hit your arm, but pass well in front of your face.
As far as not actually aiming, but just pointing your musket at the ememy, looking away and pulling the trigger; I think that theory doesn't work on a lot of levels. Why would soldiers train, not just in proper drill, but also marksmanship, only to disregard that skill at a moment when it could save their life.
The Smyth manual states: "FIRE. Press the fore finger strongly on the trigger, without lowering the head, turning it or moving the piece. "
I think a lot of the flashing problem, thus the need for a modern flashguard solution, is the lack of real training and disipline in this type of warfare. We only do it a few weekends here and there....they drilled everyday. We tend to regard manouvering in the line as a silly marching band kind of exercise, not intened for 'real men'... but in this sort of warfare, the drill is how you conduct the battle and precise execution of movements under a skilled officer is critical to victory and personal survival.
Tom