Realize that the main thing is to get the highest temperature of the water. This is close to where the water exits the engine heading for the radiator.

Often there is a water port leaving near this outlet/thermostat that feeds a full flow heater core. Often I put a short nipple at this point then a Tee then whatever it takes to continue the plumbing on to the heater core. I then screw the sensor into the Tee.