Hello, I need clarification about attacking VTOLs because some of our members are using mixed forces (mechs, vehicles, VTOLs, infantry)

On page 36 of the ASCE, the rule says:

"A unit with an elevation (from VTOL and WiGE movement, for example) is considered physically at that distance above the play area for all purposes. These units are usually left represented on the “ground” level, but for all game purposes the miniature, including base, is considered to be a number of inches above the ground equal to its elevation."

So this is an actual example that happened in gameplay: my opponent decided to elevate his VTOL to its maximum Movement at 26 inches (physically 13 inches from the ground).

My ground-based mech's hex base is 10 inches away from his VTOL's hex base base.

Do I measure just the elevation at 26 inches (i.e., like the long side of a right triangle) and disregard the 10-inch distance from my mech's hex base to his VTOL's hex base?

Or do I add the 10 inches and the 26 inches together (i.e. right angle)?

Please advise. Thanks!