These battery stats on my 6a has been... interesting...
I've been using the 6a since the start of this year, and alongside it Accubattery to remind me to unplug my phone whenever it reaches 85% charge.
I know Accubattery stats are just an approximation, and I've only been using this phone for half a year, but still quite amusing to see the battery health go up instead of dropping.
You should let the battery go to zero and then charge to 100% from time to time, even though it's stressful to the battery.
Accubattery recommends once a month to avoid these kind of odd values I believe.
My oneplus has a charge limiter that i set to 90% so it never goes above it and i have an app from fdroid called batterybot that alerts me when my phone drops below 30%. So my phone spends 99% of its time between 30% and 80% charge.