It is a shame to hear about the lose of your PSU. My condolences.
The PSU manufacturer most likely placed the thermistor on the coil to sense the ambient temperature of the coil. I appreciate the coil gets hot very quickly and therefore can only assume the coil sensing is a bandaid solution.
I wish to caution you on your idea. Do not move the thermistor too far from the coil. Placing the thermistor too close and the fan will always running @ max rated speed. Too far away, the PSU may not receive adequate cooling and the PSU may be damaged.
You might need to experiment with the placement to acheive the best results.
Good luck and good computing.