Not sure where you're getting needing only the figure in range from, as it's incorrect. Distance is always measured from and to bases.
Adjacency is the same as engaged, but both are described as figures being on a hex within 1 space of each other and not an amount of levels higher equal to or greater than the lower figure's height.
The reason I said adjacent and not engaged is that technically you can only engage opponent's figures, whereas you can be adjacent to your own and can attack your own. So they're *mostly* the same thing, but not completely.