Because the seasonings in ketchup vary by brand, using any other brand will change the flavor of the final product. (Jeffrey Steingarten describes his own extensive ketchup taste testing in "Playing Ketchup," first published in Vogue in 1992. No, we don't read Vogue--he reprinted it in The Man Who Ate Everything [Vintage, 1998].)
We use Penzey's medium chili powder. If you use a "regular" or mild chili powder, increase to 2 tablespoons.