: Does anyone have dimensions for a comfortable size and distance
: apart, for where the knees should be?

Depends on deck height, coaming width, and the lenght of your legs.

The curve in the underside of the knee hooks should be parallel to the boat's centerline. You want to grip with the inside of your knee, and if it has any aggressive (deep) shaping, it will hit your upper inside calf and upper inside thigh equally--again, you want the curve parallel to the waterline--this is also the direction in which you'll be torquing the boat--about this centerline--when you brace, roll, or edge.