Are there no rules for determining vertical occlusion for LOS?

Like if one mech is on a plateau group of +4 hexes and the other is one hex away from the grouping and 10 hexes separates both (no partial cover), LOS is "clear" as far as the rules are concerned?

I mean, I get firing weapons on a curved trajectory, but there wouldn't exist a visual for either of these units? (Indirect fire notwithstanding)