The wort throughout the bucket is going to be constantly trying to achieve a temperature equilibrium, so it's not like it you will have any concentrated "hot spot" in the center.
If you've checked the accuracy of the stick-on thermometer and have confidence in it, that will give you a decent approximation of the wort temp. I have avoided using any kind of probe into the wort since I don't wish to needlessly increase the risk of infection. I tape the temp probe from my controller on the side of the bucket and insulate it with bubble wrap.
Good Temp Control -----> Happy Yeast ------> Tasty Brew