[JesseK]

Why would you compress it any more than what you need? What advantage do you gain in power or precision by compressing the ball? Ergo, compress it only as needed. There's no specific amount; it will take prototyping. My recommendation is to measure the ball uncompressed, push it in with your palm to compress it just until the contact patch firms up a bit, then measure again. Start with that, then adjust in small amounts for your specific shooter.