Most customers use a standard printer with 8.5x11 paper, not 4x6. Giving them a 4x6 label makes them have to mess around with settings to get it to print nicely, and sometimes they just print the label to span the entire 8.5x11 paper because they can't figure it out.
Currently, if you have 4x6 set up for printing outbound labels, return labels automatically get that same format. I'd like to be able to change the Document options on just return labels to 8.5x11 but there is no option to.