**NO TO CPU SENSOR PLACEMENT**Did you read what robotdino304 was asking properly? The advice you confirmed about the CPU sensor placement was incorrect. In fact if you placed the sensor between the CPU and heat sink as he asked it would not let the cooler properly contact the CPU heat spreader and would CAUSE OVERHEATING!. To clarify, your confirmation of advice probably fried his CPU. The only place you are able to put these type of sensors is on the edge of the heat-sink close to the bottom and secure with thermal tape. Also as the heat-sink is transferring the heat from the CPU you would get nearly an identical reading as if it was touching the CPU heat spreader without toasting the CPU.
Yup, I'd say that one goes on the metal plate side, seems the best place for it to me,
and yes to the Cpu sensor placement
Most motherboards these days are able to display direct internal CPU temp (also M/B, HDD, VGA) obtained from the bios in windows and this is a much more accurate way to obtain internal CPU temp. In my experience case mounted temp sensors are just a gimmick and usually found on lower end cases to jazz them up a little and quite often cause over heating caused by improper installation by novice users.