Take the damp-towel-wrapped tortilla stack and place it directly on the oven rack. No baking sheet needed.
Why on the rack? Because it lets the heat circulate evenly around the whole package. A baking sheet can block some of that cozy heat.
It feels weird, I know. But it works. Just don’t let the towel touch the heating element—that’s a fire hazard and a very sad way to end taco night.