I have posted in suggestions to make fiefdoms worth keeping. Even if you shift around the war boosts, it still doesn’t address the issue that by the 3rd day, probably half or more of the teams will just want to drop fiefs. Additionally even when winning it’s more fun to go all out, rather than trying to win with at little fief as possible.
It would be more fun for everyone, if even on the 5th day whether you are +5 fiefs, or -2 fiefs, you still want to try give it your all to win as many as you can.
strategically more fun too trying to gain every 1 fief, trying to outmaneuver other alliances, rather than alliances contacting each other to see work out who wants to drop fiefs or not.