Is Flux an Assumed Treatment for Heated Rubies?

I had a well known color dealer (not on Poly) tell me today that traces of flux in a heated ruby is an expected and standard treatment. Since answers may depend on the level of flux found, I am referring to a GIA comment of TE2.

Poly Member 88451

Flux is most definitely expected to be seen in the heat treated Burmese (Möng Hsu) and the Mozambique rubies. GIA uses the LMHC Information sheet #1 for their grading system that makes a judgment call on the amount of flux seen. In a heated stone graded just TE you would not expect to see any flux, even though it was there when the stone was being heated. Often times a stone like a TE3 is mistaken for a flux grown synthetic. Fluxes will usually consist of Borax or other borates, glass flux, cryolite, alumina powder and sometimes chromium powder. They manifest themselves as unusual healed residues within the stone.

Poly Member 3851