On many motors, the sending unit for the gauge is located near the outlet to the top hose of the radiator.
What many do not understand is the temps you are seeing are temps of coolant that is leaving the motor, not what's in the motor. The coolant is at hottest point as it is leaving. So if the pump, fan, radiator are doing there job then the coolant temps coming in at the bottom hose should be 15-20 degrees cooler.