In the image below, the area of suction is broader and covers more surface area, covering her labia, hood, and clitoris all together. The image above shows a much smaller area, focusing in on just the clitoris only.
“To build your skills at sucking, pucker your lips to make a fish face and practice sucking the tips of your fingers. Adjust the tension in your lips until you have a good amount of suction. You’ll be amazed at how hard you can suck. Essentially, you’re using your mouth to create a vacuum, and you can create different sensations by moving the vacuum around your partner’s clit and vulva. Wrap your lips around your partner’s clit to create a good seal. Once you’ve created enough of a vacuum, you can vary the sensation by changing the amount of suction, creating a pulsing sensation. This is not very different from sucking on a nipple like you are trying to get milk out of it. Imagine you can suck some- thing out of the clit. Suction toys are a big deal in the sex tech community, carving out a whole new niche of toys that are super popular. One of my favorites is Sila from Lelo, a sonic massager and suction toy in one. Suction is super effective, and some women prefer this sensation over vibration because it feels more natural.” – Excerpt from Beyond Satisfied by Kenneth Play, Chapter 11: Oral sex, Pleasure Sucker