I don't believe standard injectors can keep up with 20 psi. I run 19 psi peak on T3 and I have Bosch greens. Cosworth standard injectors on Stage 1 usually see maximum of 15 psi. On Stage 2, as said, you need Bosch 803 (green) injectors, 3 bar MAP sensor, -31 actuator and for extra security, stronger head gasket.

I wouldn't risk running 20 psi boost with standard injectors, you might get the mixture too lean and blow up the engine. Fit greens and required chip for it to be safe!