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Here's a before and after on my phone. You can see where the rate turns down after I changed the setting. That rate of discharge is much better than what I was seeing before though.
So right now it looks like:
1) optimize on, background on = highest drain
2) optimize off, background on = less drain
3) optimize on, background off = least drain, but unreliable
Any other answers to this? I have Tesla constantly running on Android 9 with Pixel 2 and Pixel 3. It also appears if you try and turn optimization OFF, it locks out background so that cannot remain on.