I have also made this by adding a bit of garlic and both with roasted and just plain chiles (never boiled as suggested here) emulsified with oil. I also add lime juice. And use sunflower oil or even soybean oil but haven't tried Canola since I never use that. I don't like it with olive oil cuz the olive oil taste comes through in the salsa too much, but I think one place at the downtown farmer's market does it with olive oil. I like the one I make at home and of course El Pollo Rico's best.
Also saw this recipe on CH once that let me know I was on the right track.
I <3 <3 <3 that sauce!!!!! Know yall do too so just had to share!!!!