I wish to have as accurate a map as possible, and not create a rift between Avalonia and its mighty ally Kaliphilin.
Lord Khelperth -- as Dextrus Flagg says, it's probably no big deal where the border is exactly, as cartography in our medieval time is certainly no exact science. Our map of the Siccus Badlands does not even have a border drawn on it yet.
However, since Dugal MacLean and his clan have staked a claim at the mouth of the Red River, and pledged for Kaliphlin, we should probably keep it north of the river's mouth. My best guess would be, on your map, that the border starts on the coast just north of small, green island below the word "Ocean", and runs approximately due east until it reaches the point where the Red River crosses the Barqa-Avalonia road, just south of those mountains, which we have always considered to be part of Avalonia. From that point east, we would probably agree with the existing border on your map.
By the way, does Avalonia's capital city have a name?