I think that when game shape is calculated, the most important variable isn't the number of minutes, but the starting game shape. Which, in my opinion, is why the first week is very difficult, since the starting game shape is always 7. Again, this is only my opinion, if the player has game shape 9, there's a wider range of minutes which will keep his game shape up, and then as you go down to 7, you need to be much closer to the sweet spot.