No, you are misunderstanding me (or I mis spoke). Im saying you can be 400' above the ground directly below your copter. We are probably agreeing.
I think we are saying the same thing, but to me there are two different viewpoints. Here's how I interpret it.
To keep it simple, Figure 1, below (not to scale) is how the DJI app measures your altitude. It measures it from the point where you launched the drone. If it were up to them, you wouldn't be able to fly above the dotted line. Now, if you take off from a different spot, like halfway up the mountains, then your 400ft ceiling would be raised. To reiterate, that's how the DJI GO APP measures your altitude. Everything is measured from where you take-off and
the measurement doesn't change as you fly over higher or lower ground.
Figure 1:
The FAA guideline, however, can be interpreted such that you can maintain a 400ft max elevation above ground level.... period. This means the dotted line rises as the ground elevation rises, or lowers. DJI imposed a 1,640ft (500 meter) limit overall as they feel this is a reasonable ceiling to prevent people from getting into trouble with their drones. In short, that means you can go up to 1,640ft high (from your take-off point), as long as you don't go over 400' AGL altitude at any given time (to remain within FAA regulations/guidelines). See Figure 2 below.
Figure 2:
But, what about if you take-off from the top of the mountain and fly straight across the valley?
According to the FAA guidelines, you would be flying too high (more than 400' AGL in many spots), yet your flight logs would show that you were never above 400' altitude. This is where I think things could get 'sticky'. See figure 3.
Figure 3:
The bottom line is there's some work to be done if the FAA expects to be able to enforce their 'guidelines'.
Does all this make sense, or am I delusional?