I'm no boot fitter, but it seems to me that if the two cuffs were at two different angles, the boots would feel off and could cause a sensation like the foot not being flat. That's not to say that the boot fits or doesn't need work or that whoever is giving you advice knows what he's doing; I'm just saying that it's worth seeing what changes now that at least the cuffs are presumably at the same angle to the ground.
And I agree with others on the thread that the cuff angle has nothing--nada, zero, bupkes--to do with cant as the term is used in boot fitting. Head is going by the dictionary definition, which is the angle of anything relative to the ground, and probably does it deliberately to makes the buyer think he's getting the equivalent of what a professional would do for him. In boot fitting, cant refers to the angle of the whole boot to the ground, so by definition the adjustment has to come from the bottom of the boot.