Article 406.8 covers the question. Per usual it's up to the AHJ to define. In this area an in-use cover is never installed on new construction exterior outlets, and is required on all pool-related outlets.
The enforcement of 406.8 here falls more into the area of 406.8(B)(2)....depends on the intended use.
The "rule of thumb" I was taught was to considered the area under the eave, within a 45-degree area, to be "damp." So, in your example, a 30" overhange woud create a "damp" zone for the top 30" of the wall.
Unfortunately, I have absolutely no "official" substantiation for this rule....yet!
What about during a hurricane. Last year after hurricane jeanne I get a service call that gfci circuit tripping. The circuit feed outdoor and garage recp. Opening box after box and still no answer. I get to the last one that is chaulk, painted and untouched for some time. I razor knife the chaulking and paint to pry the cover off. About a quarter cup of water poured out of the box. Before I cut the cover off I did look for possible hole for water to get in but nothing but a little pin hole on side of cover in the chaulk. That meant the rain was diving sideways so hard it penetrated a hole the size of a ball point pen. The problem was cleared when the water was removed. Under normal conditions the water would never have gotten in the box. But, now days in florida hurricanes are getting too normal. Even with a good size over hang some damp areas become wet. In the 20 years in the field and 6 years as an EC, almost always the problem with water and outdoor outlets in not the opening to the outlets, but the seal behind at the wall or box. In-use covers just look good. Tom
I agree. I use the snap covers on the receptacles around my house, unless they will have unattended cords in them (only a few). I know it is technically a violation but driven rain is a problem on those bubble covers.