Org, are you sure all the WP turns to RP when heated? I know red P turns to white by heating, but I thought WP turns to the red allotrope mainy by UV irradiation?
I presume the equibrium for RP-WP via heat is strongly to the right, because on heating, a sample of purified MBRP, about a teaspoon heaped, and heated strongly enough that the test tube blew out into a bulb at the end (using a standard glass tube)
The formed WP was of a pale yellowish color, suggesting beeswax/honeycomb color, or that solid pale yellow honey, which suggests some amount of RP in there, either formed or unreacted in the first place, but certainly not very much.