A theoretical example (and ignore the actual numbers, I'm just making them up to make a point). The 18yo may have been at 7.1 and this weeks training moved him to 7.6 (half a pop), 31yo might have been at 10.9 and this weeks training moved him to 11 (a pop). So the 18 yo actually improved more, but as justme said, it is only because the 31yo made a pop that it looks weird.