Check the picture below.
so that's the angle of depression, namely the angle below the horizontal.
if we use a diagonal mile only, namely hypotenuse = 1, as you see there, then we can check what the opposite side will be, in miles.
how many feet is that?
well, there are 5280 feet in 1 mile, so that'd be 0.069756 * 5280 ≈ 368.31 feet.
