Figure out your grill grate temp vs controller temp based on the temp you usually cook at. Then dial the controller up or down to the temp that you would like your grill grate to be, and you are done.
For example, if you grill grate temp is 350 and your controller is set at 300, knock down the temp on the controller until you get the grill grate temp to 300. It will take some time the first time, but usually thereafter depending upon ambient temp changes, you should have a method.
Other option is to replace the controller with an aftermarket one that may perform better, but also may not.