If you wanted to keep it somewhat realistic, the amount of fatigue accumulated in a day (288) should be able to be fully rested in a 6-7 hour period, so based on that metric, would the upper limit be twice the amount of the peak recovery rate? Also, would you want to keep the minimum recovery rate (quick naps) the same as current, less, more? Parabolic, exponential, linear? I personally haven't really had an issue with sleep other than light waking you up through closed blinds in room.