A trick I picked up from watching the cooks at the local taqueria: They take a handful of tortillas, dip the stack in water quickly (about halfway or less, you don't have to get the whole tortilla wet), then they throw them individually on the grill top. After about 30 seconds or so they flip them. I've replicated this by just dipping each one really quickly in water and then throwing it onto a cast iron pan. The steam from the water seems to heat the entire tortilla pretty evenly. I've only tried this with corn tortillas, but I suspect it'll work with flour too.