When the environment changes causing a behaviour to change we can never be sure of what is driving the behaviour change. For example, the temperature drops and you move to a seat that is in the sun. Did you move from cold or to the heat, or was it a combination of both.
That means its impossible to train with +R alone.
Whether something is + or – R/P is not what is the most important factor, it is the body language of the learner. The body language will give us the clues that the learner is moving away from or to something.