I ran into a lot off issues getting access to those lower outside mesh grilles so ended up settling for a two sensor install for now. When I find the time to take the bumper off I'll go for the 3 sensor install based roughly on the green positions. But for now here's what it looks like...

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It's hard to tell from the pictures but I've got them pointing straight ahead (maybe off by a few degrees) and level parallel to the ground.