Ok, I'll bite....

There is a guy I work with that I was helping understand what Aikido is. This guy is 6 feet tall and weighs a whopping 320 lbs, and is a semi-pro american football player in his free time. I am 5'8" and weigh a staggering 155lbs. After helping this fellow along and teaching him roughly ten basic and more common Aikido techniques I can say that his size makes it harder for me to control him and toss him when we "freestyle". I have to use techniques and tactics he has not been introduced to in order to get him down or locked up. And heaven forbid I attempt a technique he is skilled in because he is able to overpower me regardless because he is bigger, heavier, and stronger than I am. At times I will challenge him by resisting and applying my strength to him in order to "ward off" a technique and see how he responds and he is able to feel my flow and use it against me, very rarely does he have to apply his strength to me directly. A light tap from him is much harder on me than my light tap to him, simple physics of size come into play.

Also, it is harder for me to apply certain techniques on him as there is such a vast size difference so he knows automatically that I will be inneffective in 1/3 of my aikido vocabulary off the bat. So when we do go freestyle I am able to intermix my aikido with my other skills so essentially I am doing what would appear to be more like Shinto-Ryu or Wado-Ryu after applying techniques of traditional Jujitsu , Shotokan, or even a more modernized "art" like Krav Maga or the use of a pressure point. On the strictly Aikido standpoint of training, we both make a great uke and he likes to take ukemi from me even when he says "oh hell" prior to being thrown 10 feet.

My point is that size does indeed make a difference, especially when there is resistance and there is no cooperative uke. Try to freestyle with a larger partner once or twice to see what I mean. Before my friend became a 5th Kyu he was easier to handle in freestyle, now he is hard to handle, but I love it and I love the challenge because I learn so much from it.