One of the biggest oddities in training is in stamina. High stamina can become detrimental to a player if it makes him play too many minutes which in turn gives him a game shape hit. My suggestion would be to tie the upper end of the amount of minutes where a game shape hit would be taken to stamina. Currently, 72 minutes is the upper end of the ideal range per week. Ideally, you would have that 72 minute limit go up with higher stamina. So maybe you get 76 minutes with strong, 80 with proficient, 84 with prominent, and so on.