Water Flow through a jet

My team is currently running silumations on safety valves and have hit a snagg.  We are basically running a simulation on a water jet hitting a wall.  Look at attached pdf named example(these are test values not real ones).  We have it set up with Pressure at the Inlet and Pressure at the outlet  As long as Dimension A is around .100 " the everything looks good, but when we increase A, region B gets a negative pressure and velocity out increases drastically.  any advise on solving this would be helpful.SolidworksFlow Simulation