Wrt to your question, no, BBB diameters are generally higher, not lower.
Based on your description i think its a hop up or barrel issue, perhaps crowning. Unless you bench the gun, it's hard to compare from shot to shot just where the variations originate from. Grouping is also distance sensitive,and this is a part people really don't fully understand. A grouping by it's nature is a convergence, and the convergence happens at one point in distance. If the BBs are compared at the same distances with a set distance and hopup setup, it's possible to get misleading results. You may set the test up and at a particular distance and hop up, grouping works really well for one product and sucks for another, but, if you reset the test 10 feet forward or backwards of the target, all of a sudden the grouping is better, or vice-versa.
Like I said, I don't consider the feedback "slander"' your just characterizing your experience. I am just trying to quantify the differences, because grouping can be very subjective, as its a function of distance, barrel and hop up. And as I said, your experience differs from mine, so my interest is in what conditions lead to your conclusions, when its different from mine and others. It's how I learn and improve not just my product, but my advice to people.