I knew that some time ago and it is why I am not on this site so much anymore. The be right at all cost is getting old and it has chased off a lot of the best growers from sites like this.I admitted I don't know. So I'm taking advantage of you by tossing out things I've seen and heard. The majority of my quite limited knowledge comes from my brother, an Ex-HVAC guy.
Now, this is the first I've heard something that starts to explain things. It never occurred to me that increasing the pressure would also make it harder to pump against. Very obvious when you mention it though. And as I processed that thought my ADD said squirrel by whispering "fluid dynamics". Ahhhhh......... And the mist begins to clear.