Not that I am a master at the whole "outer V" thing...
But last time I was at MAC, the MA recommended the #259 (i.e. the big square) brush to do a precise outer V. It is on my list to buy--looks like it would solve my problems, lol. Has anyone used this brush for it?
Another technique I've seen is to use an index card or Kleenex to cover up part of your face (like a stencil) so you have a real precise V line. Haven't tried this either--I'm still a newbie! HTH.