You cannot use full deflection on all the planes.

The best thing to do is to learn a inverted flat spin on the plane you want to do a blender. Not on all planes do you put full deflection to sustain an inverted flat spin. On some planes it's only half of the servo travel or the rudder, ailerons and elevator. Or a mix of the 3.

But you are basically right though. You enter a blender nose down rolling in either direction with a none or just a little throttle. Then you enter an inverted flat spin in the same direction of the roll. First you master the inverted flat spin on a particular plane, then you add the pitch down roll.