I have a short neck and sloping shoulder so I like the Mach One shoulder rest. It’s a little pricey @ + or – $60, but it is comfortable and gets the job done nicely. As for placement, think of it more as a chest rest with the lower piece landing in the middle of your chest and the upper portion wherever it fits comfortably between your chin and arm. It should be on the front of the shoulder, not on top. Hopefully this helps.