it depends on how often you are hitting the goals that are set (weekly, milestone, and seasons). which i think is set by player type for an example d-lineman that is a run stopper has tackle goals whereas a puss rusher will have sack goals. i'm not sure but make sense to me.
what he is trying to do is offset the difficulty of achieving the top level goal by the amount of xp rewarded.
so it doesn't matter if all the teams or none of the teams are human controlled. if you are crushing the goals at certain positions or if the top season goal for an example is hard to get for certain positions then try adjusting the skill sliders