It's best to start the injection pulse just after TDC when the piston is starting its intake stroke. The size of the injector is not a concern at idle because the pulse width is small and you have a lot of time. At higher RPMs the injection period will start to overlap the engines cycle but that doesn't matter at higher RPMs. The Holley system includes a way for computing the optimum injector end time based upon camshaft specifications. It's called Injector End Angle calculation.