For further research look at some dog brothers or FMA martial arts and their whole triangle step system. They step in at an angle and back out at the opposite angle (draw a lambda (this: " ^ ") go in one side, out the other). Guro Crafty Dog explains this best...(Woof!)
Slips n Fients, Keep your hands up explode off your back leg, immediately step outwards. If you watch Zambidis it's almost a circle step. He's one of the best counter fighters in the world. He baits you (the taller opponent), forces you to move forward, strikes (crashes your range while you're moving/striking), then moves back out to your appreciable range unless he hurt you then he'll bring the thunder, but he goes back out usually to avoid the clinch/knees of taller opponents.
Watch this one around 5:44 or so... Used correctly you can set up cut kicks, superman punch, or just a nice solid round kick to the ribs. Something to play with...
For MMA purposes watch none other than the angle destroyer: Shogun
Watch the videos, note the differences in each technique set and also the similarities. Being the smaller fighter there will be times that you need to increase your movement to a frenetic pace. You NEED to be able to explode, so your conditioning will be very important as well. You either need to be more powerful or much much quicker. Either can be trained to the apex of your genetic potential but just be aware which you have a natural affinity towards (or a comparative advantage against your opponent).
Some more fights to watch:
BJ Penn v Frankie Edgar I & II
Tommy Hearns v Sugar Ray Leonard
Holmes v Tyson
Any Hatton fights
Any Jose Aldo Fight
Fights Miguel Torres has lost (he's usually taller than everyone in his division)
Melvin Mahoef is usually undersized (height) compared to his opponents
Albert Kraus has the same predicament
Michael McDonald is a master in this arena, at 5'10-5'11 most of his opponents are 6'2+
Ramon Dekkers is someone to watch for striking period. But he fought Duane Ludwig and ONLY could punch this his left arm (tore ligaments in right arm prior to the bout) and still knocked Ludwig down EVERY round.
Stefan Leko is another K-1'er that tends to fight taller guys (bonjasky, badr hari)