Possible newb question here but what are the rules concerning how many rippers per base? I know with necron scarabs it is minimum 3 per base to count as a scarab swarm but what about rippers? I was unable to locate any details in the most recent codex but looking at the pics in the codex it seems to be 4-5 is the average. I wasn't sure if it was legal to get away with only 3 per base?