I am pretty shure it sucks air from the bottom. The thing is that the pc has another vent right below the screen, which I think is the one that pushes the hot air out.
Yes, I checked everything I just said. The vent slot under the laptop sucks air and the vent slot located between the keyboard and the bottom of the sreen pushes the air out.
If it is sucking air from under the laptop, it is probably fighting the fan on the laptop itself. Most suck in air from the bottom and out the side, you want something that supports the direction of airflow.
I keep a square of stocking material, (yes the kind women wear on their legs, and some men) and use double sided tape to hold it in place. It does a very good job of filtering the air going in, preventing internal dust build-up. Clean often. I have this on my desktops and laptops.