Flex point and bend point have been defined differently, and the same, over the years. One distinction was that when you load a shaft from both ends and then measure the max deflection point, that was the “kick point”. Based on your system, that sounds like what you are doing. The other was when a shaft is clamped on the butt end and a mass is attached a the tip end, causing the shaft to deflect. Measuring the max deflection point under this set up has been defined as the “bend point”. Truth be known, there is no set method used by manufacturers and most consider the terms interchangeable, even though there may be differences in the methods. No matter what method you use, I think you will find the variation or difference in the max deflection points of shafts, is not that great. Generally speaking, from information I have told by composite and steel shaft engineers, the max deflection points occur in an area of no more than 2 to 3 inches (in most cases) close to the center of any given shaft. If the max bend is toward the butt end of this area, it would be a high bend point, if it was at the tip end, it would be a low bend point, and if it was in the middle, you guessed it, it would be a mid bend point.
Hope this helps.