Y=0 is in the middle of Y_Max and Y_min (=-1*Y_Max) and negative value bars point down.
The lovelace custom mini graph card seems not able to do this. Is there maybe a UI card that can do this? If this is case, can someone please point me in the direction of the solution; maybe even share a configuration example?
You can use Grafana+InfluxDB addons and generate iframe url to create card in lovelace. that´s the way i would do.
i dont know if is there a custom card that generates it directly to lovelace.
Edit:
created the card to show how it would appear on lovelace. if you have the right entity sensors and monitoring right phases/loads, thats what it would look like
no i just got the url from share>embed and paste to webpage card, probably you are getting from share>link. see below which part of the embed url you need to copy to the card.