Unless there is something specific about the injector that is better for spray pattern or atomization (and assuming the others were not defective), there is not really a good reason to expect a performance increase in this situation.
The computer is still running the show and it merely controls the injector duty cycle to satisfy the demand.
It should run neither richer nor leaner unless the range of operation is outside of the fuel pressure and or injector capacity. If the injector is larger than than the original, the ECM recognizes more fuel and reduces the injector duty cycle to bring things (air/fuel ratio) back into balance.