I guess since you are sanding already that you have them apart already.
The best temps i like is 250-300 degrees as it is not hot and takes about 5 minutes before i start to pry slightly ,then retry ever few minutes after heating again.
Make sure you remove all clips bulbs and small plastic pieces before inserting into the oven.
Sorry it may take alittle to sand it down , Also make sure you use a flat sanding block to reduce optical distortion. A palm sander would speed up the process as well.