Rating system for online games in Heroes of Might and Magic IV.

You are right in some aspects. It's possible to implement limits for the coefficient based on Gw-Gl. For example, if a player already has a substantial rating, the coefficient could be reduced, say from 10(Gw-Gl) to simply (Gw-Gl). The same applies to players with low ratings. Rating limits could be established, and the coefficient between Gw-Gl would depend on these limits.