Well IMHO the stock fuel pump can handle the fuel demmand @21 psi but not without raising the fuel pressure.
Do a research here on the crossfire forum.
Boost pressure is "fighting" against fuel pressure. The more boost, the more fuel pressure is needed in general, especially when the pump is not big enough.
Raising the pressure to about 4.5 bar would probabely solve your problem including not to change to bigger fuel injectors/fuel pump.
I would check the pump as well (free flow). As far as i know the pump flows 160l/hr, but please recheck.