Match your use: if you’re blending into a sauce/salsa, choose a dried-chile (or ground) option that rehydrates well.
Start with the listed ratio; if your dish is sensitive (tacos, light salsas), use the lower side and build heat gradually.
If using whole dried chiles or dried flakes, briefly toast 10–20 seconds, then soak 10–15 minutes before blending for a smoother, less gritty sauce.
Simmer the sauce 2–3 minutes after adding the substitute to round off harsh spice notes.
Taste at the end: for more chile flavor add a bit more substitute; for more heat add cayenne in tiny pinches rather than doubling everything at once.