By itself, the meat is pretty spicy. The real heat comes from the tepin peppers, which are hotter than Habaneros, so you could cut back on those and add to taste. The chili powders are for distinct flavor and color. The Top Hat is a blend, the others are straight.
Masa is corn flour, lard and water and is a thick but spreadable dough, and the steam time on the ones I make is 60 minutes. Those factors kill some of the heat. Because of their size and seasonings, my tamales could be called Tex-Mex and are popular in Northern Mexico, Southern Texas, New Mexico and California. You can see the amount of meat and the meat-to-masa ratio I use. If they were super fat tamales, they would be spicier after steaming than mine are.