No problem with your English, better than many native born.....
I have heard the 30% rule before (actually just have heard "oversized"); and it is surely better for the charge pump to be oversized than undersized! And yes, it is correct that the charge pump will be feeding two cylinders rather than one, for a time.
So yes, I think it is agreed that oversized is good, I'm just thinking about the limits: where does oversizing start to hurt performance and why.
I recall as a young hand in the oilfield having suction valves pushed open so forcefully that the discharge stroke could not close them anywhere near in time and a very appreciable amount of flow was lost (as well as very rough treatment of all parts concerned). In this case, we would put either a stronger spring, or double spring on top of the suction valve to make sure it closed quickly. But we were young and dumb, and that made the problem go away so we never considered further. The point is, there is a line you cross when oversizing the charge pump that can make bad things happen.
Mainly, what I don't get is why there have not been more published studies on exactly how to properly charge a recip. There are hundreds of incredibly intense technical papers written around every imaginable topic on the suction side of a centrifugal. Not so with the poor recip pump.
Again, I say people are scared of acceleration head.