You are correct and there is a perfect explanation for it. I know you like numbers and math, so do this: Read up on Bernoulli's principles in articles such as this
https://insights.globalspec.com/article/17606/back-to-the-basics-for-calculating-fluid-flow-through-an-orifice-plate#Fluid Flow in Pipe and The Conservation of Mass#:~:text=Consider a steady flow of fluid in a pipe
It's dry, it's boring, but I promise a small light bulb will turn on when you (somewhat) understand it.
Here's the key. On the flow bench, the depression (the difference between pressure at the inlet to the port and the pressure in the cylinder itself) is usually set to 28 inches of water, or about 1 psi. So that gives you a certain amount of energy (or driving force) to work with. There is a limit to how much flow you can get. Bernoulli's equation helps define that limit. Dig into it.