I think the arc 19 could be something like "Atsuyou, Rouyou and Gyou". That would enable us to conclude arc 18 with the encirclement of Gyou and just before those battles even begin. As it is it has too long sections from that point on.
Also it would allow us to follow the events of the manga more closely when detailing the details of those battles in arc 19.
I already posted that as comment at the bottom of the "Western Zhao Invasion Arc".
What do you think?