Placing a flow modifier on a package substrate to create two flow fronts on a molded matrix array package. A flow modifier may be laid on a package substrate to a height that blocks off the bottom of other substrates (e.g., dice) coupled to the package substrate. By separating the top flow front and the bottom flow front, this process prevents the top flow front from wrapping around the sides of the substrates and trapping air below each substrate and in front of the bottom flow front.