Not many people grow on a large enough scale with enough laboratory control to truly make comparisons of growth patterns in their own environment. For example, there certainly will be strains that do better in your own environment, either indoors or outdoors but how many people actually go through these traits when buying seeds in the first place? Not many percentage wise.
Unless strict controls and measuring is done then it is always a guess in reality to the potency. With yields then that is again largely dependant on strains suiting that environment but influenced by the style of grow and the growers experience and yields will almost always improve with experience.
There have been some studies recently where it has seemed initially that there is a point of diminished returns once they reach a certain size. This seems to be when plants are actually 'exceeding' their 'natural' growth potential. I find that interesting as it has been said for years that the largest buds, that seem to be a craze in some countries (advanced nutrients followers?) seem to have a lower thc content than its smaller siblings.