[Neil]

I am sure Walter will clear this up for me.

I thought the reason smoke alarms were fitted flush to the ceiling was to do with the way the smoke rises up and then follows the ceiling as it spreads out. By having a smoke alarm hanging 6" from the ceiling it may take longer before it activates.

I know the instructions tell you how close you can fit them to walls and the corner of rooms due to the way the smokes "flows".