On my car the upper right corner of the radiator is the coolest spot. This has been true with the old and new radiators and two switches that I have also tested. The 80/88 temperature switch doesn't kick in until the car is too hot.
The 80/88 switch doesn't activate in normal operation with OEM fan, shroud, and clutch - only with the A/C. I don't really trust it enough to rely on it alone for cooling. The important factor is engine temperature, not radiator temperature. I would put a temp switch in the head or thermostat housing if I was using an electric fan by itself. Maybe it's just my car or radiator but as I mentioned, I have had the same situation with two radiators and two switches.