Bonneville Power Administration flow arrows point in wrong direction

[the-red-lily]

Describe the bug
Some arrows for flows in/out of Bonneville Power Administration appear to be backwards.

Some, such as to Nevada Power Company, point in unclear directions (though this may be representative of the underlying infrastructure, I'm not sure).

To Reproduce
Steps to reproduce the behavior:

1. Go to https://app.electricitymaps.com/map/zone/US-NW-BPAT/live/fifteen_minutes
2. Compare import/export data to direction of arrows on map (e.g. with Pacificorp West)

Expected behavior
Arrows should point in the direction of import/export.

Screenshots

Desktop (if relevant):

• OS: Windows
• Browser: Firefox

Related issues
Possible relation to #5437

[the-red-lily]

Bonneville Power Administration is a bunch of isolated polygons, so I'm guessing the arrows are relative to some center of mass of this shape or something. This leads to misleading behavior on the directions of the arrows