I learned this little trick from my old instructor Colin cannon. He taught it to me when I was 12 years old. It has helped me a lot in tournaments as well as class. Expecialy at the lower level because people are so eager to advance position.
If you make a position seem like there is no threat a lot of people will fall right into your trap and take the bait. Just be ready to turn your hips to get back to a half Guard and not just give up the mount haha
Some things to keep in mind. You don’t always have to put your legs flat you can just as easily hope they go to mount and do the same motion. You can also just put one leg down if you don’t wanna be as risky