MDMA is almost always in HCl form on he streets. The MDMA you are testing is not simply MDMA, it's actually MDMA.HCl, one molecule, a salt of the freebase MDMA. So in a way the more HCl you have in a sample the more MDMA is going to be in there as they are always bonded together. IIRC it's always 84% MDMA and 16% HCl. So smoke doesn't really say much, it's just an indication that there is a drug in there in HCl-salt form, like MDMA. Smoke can be an indication of potency but it could just as well mean that the MDMA wasn't mixed properly and that you just happened to test part of your drugs that had a concentrated spot of MDMA in it. However if the colour indicates MDMA than smoke can be an extra confirmation of the result