It does require more embouchure control, but much of the strenth is in the air column behind the note. The real work in developing the air column with enought support (potential energy) to keep lips vibrating from a diminished flow of air (volume). To keep the energy constant, pressure must adjust behind the air column (not force but pressure). You still have to control titrating the right amount of air flow to keep the note quiet. Work on the excercise as recommend by VB (an excellent methodology) but then try to added the respiratory reserve behind it as I noted in the thread above. Combining these two approaches, I stronly believe will enhance your success at playing the quietest of notes possible.