Calibrate the air pressure gauge to the water pressure gauge. Setting the air to 5 PSI less than the kick-in is fine as long as both gauges are calibrated. It sounds to me like they are not.
Turn off the pump and drain the tank just until you hear the switch click on. Then read the air pressure on the bladder and compare that to the water pressure gauge. Set the kick-in based on the air pressure reading to ensure it is 5 PSI higher.