Gotta use the tip more. Not because of any risk, but because you get the job done better. You don't really lick when you're eating pussy, at least not for the entire thing. It's all about movement and suction being used in a steady, repeatable way, with just enough variation to keep it from becoming over-stimulating.

Even when you're working the clitoris while applying suction, you don't really use the flat of the tongue. You just use the first inch or so, the way you might if you were drinking from it.

Mind you, every woman is different, so there's no single "recipe" of what's going to work best, but most women tend to enjoy a ramping up of speed, pressure, and suction as they process through the arousal cycle. If you're licking with the flat of your tongue, it's really only going to work well in the very beginning, as a break for your mouth, or as a break for them between orgasms.

Using a barrier does make good technique harder, particularly with suction. But it can be done. And, tbh, if you're with a one night or other very short term partner, good enough is good enough. So you use the barrier and make up for it by being willing to keep going lol.