Bigger size and taller height will always be an advantage in any melee-range martial arts style combat, assuming that skill-levels between the two people fighting are the same, but the higher the skill-levels of two equally skilled fighters, the less and less the size and height-difference will make a difference, although the taller guy still has more advantage of being able to land more techniques at greater range whilst the shorter guy can still gain other advantages through other means depending on his type of training. Personally, from my experiences, when both fighters are equally skilled, with the exeption of significant differences in size (such as a 7ft man against a 5ft dude), such to the point where they are both countering all of each other's attacks, the one with the higher level-of-endurance will win. I speak as a qualified martial arts instructor by the way.
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