I'm not familiar with what RPE is but the received dose of an odorant during free breathing would yield a variable concentration to the epithelium depending on effort i.e. respiration rate and volume of breath. Using peppermint will also stimulate the nasal epithelial cold receptors of the trigeminal nerve the stimulation of which may also mediate the olfactory bulb. You are acting on two systems not one. I assume that lavender has little or no trigeminal stimulatory capacity.

RPE is rating of perceived exertion, measured on the Borg scale and can be used to determine exercise intensity levels or intensity of training sessions. Further reading on my part has eliminated lavennder as being useful in this field.

What, exactly, is your protocol? It sounds like an interesting idea.

Hi Mary, there is a paper published in The Sport Psychologist that sounds very similar to what you are looking for. http://journals.humankinetics.com/tsp-back-issues/tsp-volume-25-issue-2-june/olfactory-effects-on-attention-allocation-and-perception-of-exertion

Hope this is useful.