If you shave your moustache area via the Coup de Maître it is the same principle,

I use facial expressions to stretch the lower lip taut on my teeth,

I come in at probably a 75 to 80 deg. angle and roll the razor in the same fashion as the Coup de Maître.

On around my third attempt at this I got one of the worst cut's I have had using a straight,

I have not made that mistake again.

Now that move (sans cut) is second nature.