You should check what is the limiting factor in your design.
PVElite shows this in (I'm not 100% sure about this so don't shoot me if I'm wrong) the vessel design summary.
It can be the nozzle wall thickness itself, or the nozzle reinforcement.
If it is the nozzle wall thickness, you should use a thicker pipe for the nozzle. If it is the reinforcement, you can add extra reinforcement. You should check the applicable code however to see how you may add that extra reinforcement.