Are you using extra hot Chilli powder ? Put 6 tablespoons in a Curry & it will be hot enough.
Alternatively touch Chilli powder on the tip of your tongue, then try it with a chilli (don't do it with a Scotch Bonnet ,you`ll regret it !!)
Also i`ve noticed the cooking process takes away the heat . I have tried putting 6 tablespoon in at the end, & end up with more heat but can taste powdery if put in too late, but this is also true with the spices we use. Put a teaspoon of Garam Masala at the end of cooking to give flavour.
Chilli's give a more instant heat while powder is gradual & has a warmer
taste.As you see its difficult to describe as we all taste & perceive in a different way.Hope this helps a little.