The key to forcing heel hooks and toe hooks is thinking about what they do fundamentally different than placing your foot. Toe Hooks and Heel Hooks are PULLING forces. Whereas, typically, a foot placement is a PUSHING force. The exception is a rock over on a foot where you are pulling in with your calf, although your toe is on the foot hold and you are pulling with it.
Force heelhooks easily by using them to create compression against an opposite facing edge, or sloper. Without the compression afforded by the hook move, the handhold should be useless, at the grade intended.
This is just one idea, play around with it, see what the heel hook is doing to make the line work. And play around with it on different angles. Forcing techy hooks on vertical wall can be difficult, but really fun as a lot of people don't expect it!
I have attached an image to explain the concept, but remember, setting isn't about "setting by numbers", use your creativity to take this and run with it!