What bonuses do you receive when attacking from high ground?
Solution 1:
High ground does not confer any attack bonus. It simply means you can shoot the enemy without them shooting back (unless they have an air unit or other means of "seeing" you up on the high ground.
Double-high ground does not confer any bonuses beyond high ground. The only difference (that I know of) is that jumping/climbing units like Reapers and Colossi cannot scale a double-high cliff - they have to climb one level at a time.