Nope, that's not it. The point of using the 2.2 pistons is to move the pin bore up, allowing a longer rod while keeping reasonable compression. And the reason you'd want to do that is to get the advantages of a better rod/stroke ratio: longer piston dwell time at TDC (= more cylinder pressure develops before the piston starts to move down = more zoom) and less side-loading of the pistons against the cylinder walls (=lower frictional loss). The rings those pistons take are also thinner, which also contributes to lower engine friction.