I'm installing a furnace and a/c coil horizontally in a crawlspace. The furnace is at one end of the house and a trunk line runs to the other end. All of the heat ducts on the furnace end need to be snaked somehow to the plenum. This means that the duct leaves the floor joist cavity and runs perpendicular to the joists until it reaches the plenum. I can save myself 2 90's if I position the takeoff on the underside of the plenum as opposed to the usual top of the plenum. Which is better; having the takeoff on the bottom or having the takeoff on the top with two extra 90's to contend with?