We got a great volley going here.
The air strikes the underside of the wing at high alpha and negotiates the turn around the leading edge. The vortilon's position is very close to the stagnation line and it is designed to provide a vortex only at high alpha (alpha is angle of attack in American parlance, sometimes the British use the term angle of incidence). Remember that we really don't want to create vortices, because that is adding to our drag, but at high angle of attack that's okay. Is it getting any clearer? Sorry I can't write better.