I see what you mean - the flow leaving the ports is better than the stock manifolds, but it all stops when the front and rear manifolds aim at each other. What that needs is a pair of weld-ell 90° fittings, one for each dump, parallel, or (if not enough room) siamese them as needed into a "Y".
Just a thought: not practical if you already have the system built, and/or have limited room under the hood, but if 2 rears (or 2 fronts) were used, with the "wrong" one upside down on the other side, the pipes would pass each other without interference one above the other, and could simply both be turned down 90° into a dual system.
