Best-evidenced claim in the dish
33 cooks, no dissent
More chile makes it hotter. Less makes it milder. Reliably.
Adding more cayenne, dried chili peppers, chipotles, ancho powder, extra jalapeno, or a splash more hot sauce reliably pushes the chili's heat level up and is well received.
Reducing or omitting the jalapeno, cayenne, or chili powder -- or using milder chili beans instead of kidney beans -- tames the heat for those who don't want spice, without hurting satisfaction.
What to do: add in small increments and taste as
you go — two cooks specifically report holding the jalapenos back
until a mid-cook taste and then adjusting, and landing where they
wanted. Heat is one of the few things in cooking you can genuinely
titrate.
The asymmetry worth knowing
3 cooks
Halving the chili powder does not halve the heat
Cutting the chili powder amount (to about half, or to 1-1.5 tbsp from a larger original amount) still left heat level at a moderate-to-high 5-7/10, suggesting chili powder alone is not the dominant heat driver in these recipes.
Cooks who cut the chili powder to about half, or down to
1–1.5 tbsp from a larger amount, still ended up with a
moderate-to-high result. The base recipe is usually carrying more chile
than its stated heat implies, so you have more room to under-dose than
the numbers suggest. Going the other way has no such cushion.
What to do: if you are cooking for people with
different tolerances, start well under and correct upward. The recovery
from too mild is a spoonful; the recovery from too hot is another pot
of tomatoes and beans.