I have learned a lot from your book, "The Chile Pepper Encyclopedia", which I purchased a few months ago. A subject of great interest to me is to understand exactly how one pepper type is hotter than the next. From your book I have learned that the crystalline alkaloid makeup of all chile peppers is exactly the same with 69% capsaicin, 22% dihydocapsaicin, 7% nordihydocapsaicin, 1% homocapsaicin, and 1% homodihydrocapsaicin. If this is the case, then, my logical conclusion is that the relative hotness between chile peppers is determined by the concentration or density of the capsaicinoids per square millimeter of the pepper bodies. Is this correct? I could not find the answer to this technical question in the book. If it is there please let me know the page number.
In fact, the percentage of the different capsainoids varies from variety to variety, and our mouth reacts differently to each one. So the perceived heat is a result of mostly the percentage of capsaicin (all the capsaicinoids together) in each pod, plus the unique combination of the actual capsaicinoids present. The statement of the percentages is of the crystalline alkaloid (pure generic capsaicin, refined from oleoresin capsicin, not of the pepper pods. The effects of the various capsacinoids on the mouth are described on page 57. Your statement is correct, but it might be more accurate that the relative hotness of a pepper pod depends on the relative amount of capsaicin by weight in each pod. OI course, the weight of the capsaicin would be in micrograms. For example, a New Mexican chile and a chiltepin may contain the same amount of capsaicin, but the weight of the New Mexican chile would be hundreds of times more; thus the capsaicin in the New Mexican chile would be diluted throughout the pulp and the perceived heat would be less. The hottest chiles have the least pod mass plus the highest amount of capsaicin.
I hope this helps.