Say I have a group of four, all lv 4s. What kind of total CR monster should I give them? (well my logic so far is 4x4=16, so i can give them anything that is up to 16 either in a single creature form or in a group like three lv 4s). But last time we played, apparently three lv 3s proves to be too difficult for them. (they are all new players) Did i do the math wrong? (like i shouldnt do my math that way)