I'm not saying delidding is something to do, but I watched a video where replacing the absolute pos thermal material on ivy and haswell chips dropped temps up to 10c without changing the stock cooler. If you don't have one of those chips, it could be a lack of airflow. Make sure you are doing a pull config with the fresh air going through the H100 and warmer air into the case.
Also, if your processor is unlocked, look into undervolting the CPU.
All this is assuming you applied the thermal paste correctly when installing the H100, because the cooler is only as good as the thermal paste and application.