I have similar issues working with game shape. I have a player
(6767297) who dropped from proficient to respectable over a one week period due to high minutes (88, I think), however he has stayed at respectable after receiving optimal minutes last week (67). Also several of my players at proficient dropped to strong after receiving 60-67 minutes of training. So I am very confused as to how to keep game shape at optimal levels. I know there is a discussion of GS having other factors but to me it seems that GS has a high percentage random component not related to either stamina or age.