You're mistaken, whether the person is aware of the negative things in them or not and you speak negative about them while they're absent it's gheebah. Look into the story of how the ayah of gheebah was revealed. Aisha, just signaled in with her hand that the woman who left the room was short, and the law againbst gheebah was revealed. Do short people don;t know their height? and people are not aware of it? She left the room and the prophet saw her while she was in the room, yet that hand signal meaning she's short was considered gheebah. The only time it's negative and not a gheebah is when the talk is about a publically committed sin. Woman X does not wear hijab all the time in public. It;'s a sin, it's not a compliment, it's mentioning a sin this woman X does, however it is done by her in public, so mentioning it even if she is not present is not gheebah.