Picture #2, a swimmer with 40 degrees will have a kick that is of little or no use. To place the top of the foot at an angle that is propulsive requires significant bending of the knee. When the knee bends, the thigh moves down and causes enough drag to cancel out most or all of the propulsion from the top of the foot. The kick is not worth doing. These swimmers love pull buoys! Swimmers with less than this range of motion, when kicking flutter kick on a kick board, can actually go backwards.
This is why I am so slow in the water, compounded by heavy muscular legs.
Well there is the possibility of using the rack to improve my flexibility. I think I can build one of them myself.