ratting is having full mobility and not taking fights. You dont need to invade other peoples CDs. Majority of people who i know rat bascially never invade and run when getting invaded to break crystals. And i havent dont CDs late week, but before that i was always invading/getting invaded and never got a t3 item. This was the T6 CD.
As far as the ratting thing goes from what you said theres only 1 circumstance wherein I will ever start breaking crystals inside my own dungeon when someone invades and thats if im fighting someone who legit runs away everytime we fight. Im not talking like them kiting either im talking about me getting them low and out sustaining them and them using boots to flee to the other side of the dungeon and re-healing back up Which even at that point I break 1 crystal per everytime they run (As a means of making them come back to fight)