In one of the tanks I keep them together with cpd's (I assume cpd==D.Margaritus). D.Kyathit's form the "core shoal", D.Margaritus join them on occasions. My D.Kyathit's are the spotted kind, so the mixed shoal looks pretty nice.
D.Kyathit's need/like higher flow; so in my tank they spend more of the time in the higher flow area while D.Margaritus use the entire tank.