I believe it is species specific - at least for me.
Once I crossed the path of eating a chinense without dilution, I no longer need the coolant to be able to eat them no matter how hot, sure it can be painful but I have crossed the point of no return by eating chinense peppers.
With annumm, they still caused discomfort until recently. You need to eat a birds eye pepper whole and deal with it without coolant. You should be able to tolerate any annumm after this expercise.
But there are way too many variables to account for, I believe your immune system plays a big role in this equation, as would your body's acidity fpr similar reasons. This is partly why it can be dangerous to eating peppers that are too hot for yourself. If your heart and stomach are in great shape then there is no risk however always take into account that hot food raises body temperature, pumps blood harder, lines your stomach and does some interesting things with your brains.
My advice? Eat a red habanero, put up with it, try again until you can handle them easier, then you can easily make a jump to the jolokia. With pre-existing knowledge you will skyrocket your tolerance, but if you skyrocket it, if you don't persist your tolerance will decrease at a similar rate - which is why we include it in our diets daily when possible - apart from taste, smell, and the passion
Be responsible, but don't be shy