I have zero knowledge or experience in ama design but, as a relative OC-1 novice, some experience and observations with effects. My GPS shows that I lose .1-.2 mph when switching from my right side to my left. I attribute this to weight shift, which in turn loads the ama a bit more. This is why good paddlers will 'fly the ama'. Well, in addition to the fun aspect. A buddy, whose open water surfski experience has given him excellent balance, told me about flying his ama on a downwind rum.: he instantly dropped the other paddlers. So why not just fly it all of the time? Well, most main OC-1 canoes are about 14" wide. Danny Ching, winner of the Molokai to Oahu OC-1 race this past April, can paddle without an ama, at least on flat water, but mortals would have very short runs if they tried it.
As for ama design, my current canoe, a Huki V1X, used to have a markedly upswept ama, but the new version (which I have), is much less so. It may or may not be pertinent, but the V1X seems to be just a touch faster than many other boats on the flats, but not as good in the bumps.