The ports in the back are for some applications that need cool water, like some EGR cooler applications. The rear ports are not full engine temp, they are only after the water has run past the cylinders and not through the heads. The heads are where most of the heat is picked up. Putting a sensor in that rear crossover will give it false readings.
And yes, there are only 2 ports in the front of the intake. EFI has the sensor in the heater hose fitting, but the heater on EFI applicaions is full flow. Stock Bronco heater is thorttled water supply. I have no issues using a short T and get the sensor as close to the intake as possible. Water conducts heat rather well, there is turbulance in the water flow, a little out of the direct path will be fine. But it still has to be close enough to get the water flow and read the right temp.