Keep in mind that for distances less than 30 miles, ground wave is a likely propogation path. The exception would be a path which was less than say 50 miles, but heavily obstructed by terrain such as a high mountain or ridge line between the two stations. A table of slant path distance and takeoff angle for various high angle skips from the E, F, F1 and F2 layers over various distances from five to 300 miles baseline. This is the basic so called NVI zone, including areas blocked from ground wave less than 50 miles distant, out to reasonable first skip zone distances workable with antennas like beams on towers. Distances 5-30 miles represent contacts between stations on the same island which do not have ground wave contact, that is blocked by exceptional mountain ridges.
Angles are in degrees.
Path length is the slant height up and back down. Remember at night the F1 and F2 layers tend to merge into the F layer. The D layer which is strong during the day is not much good for skip, but it does cause a very large amount of attenuation both going up and coming back down. For two E skips, look up the total half distance and multiply the path length by two, but take the takeoff angle from the chart for half the distance.