This is related to:
http://forum.naruto.oasgames.com/en/forum.php?mod=viewthread&tid=11571&extra=page%3D1
You should stop closing threads before all aspect of the issue is examined, thou technically the point of error would be different here.
Now, allow me to elaborate, based on b), there are exactly two ways for a) to be reasonable:
1. if b) is independent of a) and the overall reward is same regardless of adjustment, in this case the exact adjustment doesn't really matter much and does not require careful calibration. But you said this is not the case
2. if b) is based on a), then the adjustment made by a) SHOULD be reasonable, in that it gives a good chance to defeat the fox while being sufficiently strong to provide both a challenge and meaningful reward, requiring careful calibration. This isn't the case in many servers, including ours, where the fox is dying under 10 minutes.
Since you say #2 is the way it SHOULD function, I can only come to the conclusion that whatever formula you are using to adjust the fox is problematic and should be fixed. IMO, proper fox should require average of 30 min to kill for "average" level of activity in the server (meaning it will die in 20 min on an active day and not at all if many people, especially top ones, slack off). 5-10 minute is simply unacceptable and make the event almost moot.