When using Mind's Eye, you should funnel all casts of Devouring Plague onto a main priority target to maximize AoE damage. While you can also play this way with Distorted Reality you will gain more overall damage if you spread the DoT around when using that talent. You can still funnel with Distorted Reality, but generally Mind's Eye is better with that playstyle. With Distorted Reality, be sure only to swap targets as you get a Mind Devourer proc, or you have enough Insanity to cast the spell so that you are still focusing a target with that DoT active for the mastery bonus.