Where should you put you legs on the leg press❓ And let's forewarn you, there is NO wrong answer! Just as we believe there is no such thing as a "bad exercise", it all comes down to the goals and intentions of the exercise.
The leg press is a great way to develop lower body muscular strength and endurance, especially for those that are uncomfortable with closed kinetic chain exercises (squats). That being said, they primarily hit the two major lower extremity muscle groups: the quadriceps and the glutes. Biomechanically speaking, you can alter which muscle group preferentially takes more of the load by altering your foot placement.
⬆ foot placement = larger hip extensor lever arm = more GLUTE � activation
⬇ foot placement = larger knee extensor lever arm = more QUAD activation
Again, while no position it technically 'wrong', we are not the biggest fans of choosing a super low foot placement in which your heel comes up during the leg press. If your heel comes up, it most likely means you're putting a ton of anterior shear on the knee, so keep that heel down (or work on your ankle mobility if its limited!)