Cadsuane probably made sure that every circle that went out into the field was at a minimum stronger than herself + her angreal (i.e. level ++1).
If you think about it that's the only real benchmark she has. She knows she's roughly equal to Rand when she draws on the angreal and she must assume that the Forsaken are going to be about at that same level so she wouldn't send a team out that didn't have a considerable strength advantage.