my conclusions:
- A Mentor has to be active to have any effect
- A player must be active (but not necessarily on the depth chart) to receive any benefit from a mentor
- Active backups will progress even without playing time in the presence of a mentor.
- Without a mentor, players do not progress at all without playing time.
- There doesn't appear to be a limit to the number of active players who can receive the benfits of a mentor
my thoughts:
The effects of mentors on starters have probably been vastly overrated. The more trials i ran, the more confident I became that the rate at which a player develops is largely specific to that individual player. One glance at the two different starting QBs in the major examples here shows us that one progressed faster whenever in the same role (be that starter or backup). Some players are simply going to develop faster than others - mentor or no mentor.
The primarily value in mentors may actually be in developing your backup players. It allows you to give them the effect of playing time (thought not at a 100% rate apparently), without them actually having to be in a game.