The Seven Foot Rule is a great rule of thumb to be safe. It's simple to remember and for most conditions quite conservative.
However, if you are on a mountainside with tons of rain in the winter months, speak to someone who is professionally qualified. Otherwise you are flirting with disaster.
As you can see in the photo, any footings on a sloped grade like this should be safe if the widest point of the footing is no closer
than seven feet from the slope when you project a horizontal line from
the point of the underside of the footing.