First I want to say that Greg is doing a really good job. I really wanted to play Half-Life: Alyx and bought Driver4VR just for that and I did it using Kinect, Android with riftcat and joy con. I manage to solve joy con drift pretty easy but my head was drifting all the time. I noticed my phone was getting too hot as well. Then I discovered that the problem was not temperature but variation! When my phone gets too hot, it reduces processing power to chill, then gets hot again and that variation of temperature causes a LOT of drift and you can’t just recalibrate. So if anyone was problems with head track drifting a lot check your smartphone!
You can try collect data from your head using other source like a webcam or just use a coolling system for your phone.