You can do an independent confirmation by using an IR thermometer and basically looking for the hottest spot you can find at your proposed location.
Here's a cheap one. Mine has been surprisingly accurate and I've had it for almost a decade now. This is -similar- to mine.
Infrared Thermometer - Non-contact, Digital Thermometer
So yeah, find the hottest spot, mount your sensor and insulate it well. You can also do a reality check by comparing the reading of your sensor/gauge with a known accurate coolant temp. Does your car not have a coolant readout? Perhaps a scangauge would give you access to that number??? I would not bet my car on a cheap thermometer, not designed for this application. Not without a lot of verification that it was telling me what I thought it was telling me.