Let me preface by saying this is a very open ended question What I'm looking for in the answer is the general approach the mental aspect of how you should fight someone like this. For example when the fight starts should you try to catch the person of guard and try to end it as quickly as possible, Should you try to lure your opponent into a false sense of security, endure and look for an opening to risk everything on? The second part is specific techniques like certain kicks or submissions or overall like martial arts styles Muay Thai or Jujutsu would be best. Another way I could to think of this is trying to figure out the best way for technique and combat intelligence to overcome physical superiority.
Assume that the physically advantaged person in question is also a mixed martial artist who has proficiency in a variety of martial arts technique. What are the best things to learn in order to best beat someone who beats you on all physical fronts?
Don't factor it difficulty of learning the techniques you recommend for the physically disadvantaged person. I want this to be about an optimal scenario where technique for the smaller person isn't an issue and more about how to use it instead of if they can learn it.