Build hamstrings that show from behind.
Keep your hips down on the pad, don't let them pop up to cheat the curl.
The leg curl is one of the only moves that trains the hamstrings through their true job at the knee, curling the heel toward the glutes against resistance. Lying face down with your hips pinned, there's nowhere for other muscles to help, which is exactly the point. Hinges like deadlifts load hamstrings at the hip, so the curl fills the other half of hamstring training that they miss.
Yes. RDLs work the hamstrings at the hip, curls work them at the knee, and full hamstring development needs both jobs covered.
The weight is too heavy and your hips are hinging to help. Drop the load, press your hips into the bench, and make the heels do all the travelling.
Pointing your toes takes the calves out and isolates the hamstrings harder, which usually means less weight. Flexing the toes up lets the calves assist so you can curl a bit more.
