My house uses flexible ducts in the attic for our heat and air conditioning. After doing some reading, I have learned that the flexible ducts should be supported with straps to keep as few bends in them as possible. Is this accurate? I have some ducts that put out a good deal of air but others that do not seem to put that much air out. The ducts run to a vent in the ceilings of my house but the vents come up into the attic vertically, allowing for the flexible ducts to bend. Would this be the reason for the less air flow in some locations? One location is at the front, not the end, of the main trunk but it has reduced air. Do I need to use straps to support the ducts or an elbow by the vent so it does not allow the flexible duct to bend? Both?