I want to just make sure that I have this right: the rules in Total Warfare (page 100) for intervening terrain and line of sight are just abstractions to make the game easier to play, right?
Because if they are simulations of line of sight, it doesn't really bear out... for instance, consider the case where 'Mech A is on top of a broad plateau, 6 hexes away from the edge, and 'Mech B could be in the canyon below, two hexes from the wall of the plateau and 6 levels down.
According to the rules, the two 'Mechs have line of sight, since 'Mech A is the same level as the intervening terrain (that is, the flat surface of the plateau) and 'Mech B is not adjacent to the plateau (but rather is 2 hexes over). In the real world, the edge of the plateau would create a huge deadzone blocking 'Mech A's line of sight down into the canyon until he came very close to the edge of the plateau.
So just so I am certain—this is how the rules are meant to work, and this is just to make things easier so you don't have to break out your rusty 8th grade geometry textbook, right?
Edit: Added pic to show the example (although the 'Mech B is only 3 levels down, to make the image smaller):