My suggestion is that when a player challenages you and you are in your own territory and you flee instead of losing energy you get a 5 minute surrender debuff.
If you flee a duel in enemy lands you still lose energy as normal and still get the five minute debuff. This stops players from running back and trying again to snipe or attempt to attack a castle.
If you are in unclaimed land and flee a duel it's just energy loss.
Also if you accept a duel you must field the power requirement you have to meet for your own castle level.
So for example if a castle 9 challenages a castle 8 the 9 must field 4700 as they do already in current game but the 8 has to field 4000 power.
This change makes i so people will stop fielding just heroes and actually play the game instead of not playing.