I have a temp sensor in line to the cooler closer to the engine.
The owner at Jaggi in Houston, Hans, told me that the fluid through the cooler reverses course when the trany goes into torque converter "lock-up". This can happen in any gear depending on where you have the shifter positioned D,3, 2,1. In D this is usually about 52 MPH.
So depending on where you think overheating is likely to occur, then choose the correct line in which to place the sensor.
For me, mine gets the hottest when climbing off road grades pulling a tent trailer. This occurs because the stock position of the LR cooler is below the radiator and does not gain any cooling air flow from the engine fan.
The fluid pipes coming from the 4HP22 can be referenced as upper and lower based on where they attach to the trany. The upper position line is where I have tapped into to get the hotter reading while in "lock-up".
Mine has never been into the "yellow" zone (250-300?F) and I have pulled some long grades in 1st gear (slowest air flow over a stock LR cooler). My gauge and sensor is made specifically for transmission fluid by WesTach. Most of the time the temp needle barely comes up off of the lowest reading