Ok, so before the Sirion interception, who do you think would have won the war? Westmoor was in control of both Commonyr and Oberndorf. Until Sirion stepped in and wanted peace for a future Nivemus to be created... So I'm sure King Jor had a reason on why to not except Fontan's rediculous "peace offers", when so clearly Fontan would be down to Krimml by now.
War is not just about armies and battles, it's about the diplomatic space within which those battles occur.
Sirion was obliged by treaty to defend Fontan's territorial integrity. Westmoor knew this as they had seen the full terms of the surrender and their efforts to keep Krimml put them on a collision course. They also knew that Sirion's key demand for peace was the right to refound a Rancaguan realm in Ashforth, so raiding that city during the conquest of Oberndorf and Commonyr further aggravated their position.
The government of Fontan used this to outmanoeuvre that of Westmoor, buying time to build up military strength, and once we'd cleared Westmoor's forces from the north we won all but one battle we engaged in on their home territory - despite still having a much smaller army at that time.
Not a single Sirion soldier was actually required to raise arms in defence of Fontanese soil so we will never know if Fontan's position was well-founded or not, but Westmoor blinked and that cost them a victory which realms have sought in the past. Since then Westmoor's government has wasted time that the nobles of Fontan have used productively to improve infrastructure, train troops, build gold reserves and generally prepare for war.
