I have seen them that way before. On one job I had to inspect the work of the installer for a chain. It was an above ceiling grid install and the specs called for the opening to be on the top of the return air duct for sound issues. They left the end open, and the heat and air sub had to come back out and change it.
sorry to respond to you here but I cant figure out how the hell to just send a guy a message on this site as upposed to posting in a forum- nice to meet you and hopefully you can help me forget this blonde moment