it has been discussed at length in this section here
tickets where handed in and the developers ensured us that its working as intended. the dragon is placed outside of his formation in the top row behind the screen, ending up visually behind your own party. he is never visible, so i am not sure what you meant by he sometimes appears and sometimes not. however since he is not inside the 3x3 field your AOE can not reach him until the top row is cleared.
you are correct about rhize since khan got a double damage reduction (retaining morale, hitting multiple positions) he does more damage than khan and blasts higher crits. however the two have different strategies in use since khans defense is higher and he retains morale. grz on defeating the boss and the rest is a piece of cake.



