No that's right afaik. When the game shape stays exactly equal, even in sublevels, then you should see an increase in DMI when the player improved in sublevels.
But you will see huge fluctuations in DMI when you got high skilled players. One week they have a DMI of 500k in a high proficient form, while they have 400k DMI the other week in a low proficient game shape. A little improvement in the trained sublevel just doesn't add up to this difference.