Capping issues in Dragons Lair using AOE skills

[Ora]

If you use an AOE skill fighting the bosses in Dragons Lair ( I used my Ranger and ignite arrows) the dragons will retreat behind the place where the portal appears.
Thus, if a warrior or a hench is attacking them, the entire party is ported to the next level and you can't cap.

[Ora]

Workaround (sry, too late for editing): Chase the dragon bosses away from the portal place