In Star Wars: Episode I - The Phantom Menace near the end, we see Obi-Wan Kenobi fight Darth Maul. Darth Maul has the high ground, but Obi-Wan wins the battle.
Later, in Star Wars: Episode III - Revenge of the Sith when Anakin Skywalker fights Obi-Wan, Obi-Wan is the one who has the high ground. He explicitly states that him having the high ground is a huge advantage and that Anakin has no chance. Anakin tries to jump over him but fails.
Why is the high ground treated differently in these two movies, especially having Obi-Wan be in both situations (having both high and low ground) and winning in both?