I don't give out comms just for players showing up to content. I give comms to those that impress me with keeping the run going smooth and fast. I generally heal content and in 4 man it generally goes to the tank cause the dps df gives me rarely does anything above the bare minimum. In 8 person raid finder it is more often I find a dps or healer that stands out. Either way to get a comm, you have to go above and beyond average. In playing I get equal comms between my healers and my blm. I do tank on drk but that is a work in progress and I rarely get comms there. I sit somewhere around mid 4000 comms. I would also wonder since you ask for a thanks, do you talk in content? I say hi at the start of almost every run and thanks at the end all runs regardless of how the run went. I also take time to explain mechs to new players where helpful.