Now the wax melts at anywheres from 120° to 150°. It would seem best to add the fragrance at the lowest possible temperature, right?
The wax needs to be hot enough to allow the fragrance oil to fully incorporate and "bind" with the wax. 180° seems to be the magic temperature. I did a test of this -- making one candle where I added the fragrance at 165° and one candle where I added it at 180°. The candle that had the fragrance added at 180° had better cold and hot throw. You can still smell the fragrance in the 165° candle...but the 180° one was just plain better. I've done this test with both paraffin and soy wax. It was most pronounced in the paraffin, but even the soy was better at 180°.