Likely because you are closer to your limit with your designs (Pushing the limit of draw length) that you've tested. Just speculation of course. Mine seem to be closer to 3 as well. This is interresting indeed. Don't you usually make longbows,adb? Arc of the cicrle tiller? Recurves will likely make a difference. All of my bows have stiff tips for the last 6" or so (modified "molly"esque designs)
