DIY Room treatments..How Large?????

Hi,
I picked up a sheet of Owens Corning and some low profile batting material for front face of panels to "soften" the face appearance, and some Natural Needled Cotton fabric to wrap panels in, I have 4...2ft X 4ft pieces to work with, I want to tame one wall, as other has a sofa along it and a quilt rack at first reflection point. I also want to place one on ceiling at reflection point and 2 on the back wall.
My room is small, 13X20 and I wanted to know if I place one 2ft X 4ft panel in middle of room on ceiling at reflection point would 4ft across be enough width and 2 ft be enough from front to back?
Also if I cant make a tube trap, could I use more of these behind speakers? or will these be less then ideal?
As far as making tubes it seems both hard to make and also hard to purchase the right suppplies with me being disabled and on a fixed income but I do want to make the best out of what I have.
So in short, will my panel be big enough for ceiling reflection?, I will also use one on live wall to tame it down and have 2 left for back wall. and if I get one more peice, and material could I use 4 more for corners behind tower speakers...as always thanks a bunch guys Regards,
Chad
If anyone would be willing to talk with me I would gladly accept, I can call to save long distance charges for help, please send me mail if any offers thanks!