Obi-Wan doesn't need to be on the high ground, the high ground just needs to exist within the battle; Obi-Wan knows that when he has the low ground, he really has the high ground, from a certain point of view; see Diagram A [imgur.com].

Look at his battle record:

Maul: Has low ground, wins Example A [imgur.com]

Dooku: No high ground, loses

Dooku rematch: No high ground, loses Example B [imgur.com].

Greivous: Has low ground, wins Example C [imgur.com]

Vader: Has high ground, wins

Vader rematch: No high ground, loses

Obi-Wan with the high/low ground is canonically the most powerful Jedi. This is fact. Had Yoda not denied his request to battle The Senate with typical Jedi arrogance, Obi-Wan could have defeated Palpatine in the Senate building, which housed a variety of different altitudes; this was designed so that the Chancellor could always have the moral high ground in political debates. But Obi-wan didn't fight The Senate, and Yoda soon learned that you can't cleave the Sheev in a normal 1v1.

Yoda is shorter than virtually every other fighter, which gives him a permanent low-ground disadvantage; however, his saber-fighting style utilizes a flipping-heavy technique in order to negate this weakness for a temporary window. You'll notice that, as he falls from the central podium in The Senate's building, he immediately retreats, knowing that he can never hold the high ground in this duel. You'll also notice that, while training Luke, he rides on him like a mount, to gain the intellectual high ground and accelerate Luke's training. Example D [imgur.com].

Obi-Wan's defensive Form III lightsaber style synergizes with his careful military maneuvers; as he only strikes when prepared, he can always hold the strategic high ground. You'll come to realize that Commander Cody's artillery strike failed against Obi-Wan, when hundreds of Jedi were killed in similar attacks. Cody failed to grasp the strategic situation, as the Jedi Master's elevation was superior to his by hundreds of meters, making him virtually unkillable. Had Cody taken his time and engaged the Jedi on even terrain, he could have possibly succeeded. Obi-Wan then retreated under the surface of the lake, so that he could maintain the topographical low/high ground. In RotS, you'll notice that all the Jedi killed were on level ground with the clones, thereby assuring their demise.

As we all know, spinning is a good trick. However, only the Chosen one can spin outside of a starfighter. Palpatine tried spinning, but he lost due to this technique (but this was intentional, as losing gave him the emotional high ground when Anakin arrived). The reason for this is that spinning provides a yin-yang approach to combat (based in Eastern philosophy on balance), giving the spinner the high ground from above and below. Only the Chosen One can master the spin, as it is their destiny to maintain balance in the universe. This is why Obi-Wan was so emotional after defeating Vader on Mustafar; he expected to lose the high ground to the spin, but Anakin fell to the dark side and could no longer use his signature trick, becoming the very thing he swore to destroy.

Anakin doesn't hate sand for the reasons he told Padme; all Jedi hate sand, as the battlefield can rapidly change between low and high ground on multiple vectors, so your perspective must be from a certain three-dimensional point of view in order to comprehend who holds the high ground. This is the only reason why Obi-Wan killed Maul in Rebels. This is also why Obi-Wan hates flying; there is no gravity in space, therefore there is no high or low ground from any frame of reference (This also negates the spinning trick, as noted in Example E [imgur.com]).

It took the Tusken Raiders years of conflict against Old Ben Kenobi to grasp his superiority in terrain advantage, as you see them visibly flee in ANH when they realize he holds the low (inverse-high) ground. Additionally, Obi-Wan's victory in the cantina against the drunkard was assured, as he held the temperamental high ground, his actions more calculated and well-thought than the alcoholic, who was so uncivilized.

In ANH, Vader proves his newfound mastery by engaging Obi on perfectly even ground. However, Obi-Wan intentionally sacrifices himself on the Death Star, so that he could train Luke from a higher plane of existence, thereby giving him the metaphysical high ground [Example F] Example F [imgur.com].

Why was Vader so invested in the construction and maintenance of the Death Star? Because he knows Obi-wan can't have the high ground if there's no ground left. Image A [imgur.com].

As seen through the events of the Clone Wars, Obi-Wan was known to be on friendly terms with Senator Organa, whose homeworld held large quantities of mountainous terrain, the *perfect* habitat for a Jedi Master. Grand Moff Tarkin was already in position to destroy Alderaan as a first target, as the distance from Scarif to Alderaan was too vast to reach between the escape and recapture of the Tantive IV, even at 1.0 lightspeed. Alderaan had been the initial target all along, as Obi-Wan with the high ground was the primary threat to the Death Star. How? Because a moon-sized space station would have some form of gravitational pull, thereby negating Obi-Wan's zero-gravity weakness; Obi-Wan with the perpetual high-ground in a low-orbit starfighter would easily be able to fire proton torpedoes through a ventilation shaft, although the Empire was uncertain of the specific weakness of the Death Star planned by Galen Erso (who was a good friend).

In Return of the Jedi, you can see that the Throne Room contains a variety of different altitudes; Palpatine placed these there to ensure Vader's defeat. However, Sheev failed to realize that his weakness was no ground, and should have covered that useless gaping pit which does nothing.

A common misconception is the idea of a 'prostrate position' version of the high ground, wherein Obi-Wan lies flat on his back, giving him tactical superiority from his point of view. However, this strategy is futile, as for the high ground to come into effect, there must be a differential between parties on both the x-axis and y-axis to a moderately significant variation from both absolutes (Angles only a Sith would deal in). For Obi-Wan's high ground powers to have full effect, he must stand between 15 and 75 degrees (π/12 to 5π/12 radians) diagonal from his opponent(s) on any quadrant of the trigonometric circle. See Diagram B [imgur.com].

In conclusion, Obi-wan abuses spatial relativity and Taoist doctrine in order to always invoke his high-ground powers.