Fluid travels on pipes based on a pressure system. If the pressure on one pipe is higher then the pressure on the next pipe, it 'leaks' to the next pipe.
Pressure is calculated by the amount of liquid / total capacity.
So, increasing capacity, you reduce the pressure for the same amount of liquid making it flow less. What you actually do when you double capacity his halve the throughput!
That is the biggest mistake people do with bobs pipes. Its not the higher capacity that give a better flow, its actually the smallest ones since they reach higher pressure faster! Big capacity pipes are good to transfer a lot of fluids on a very short path (1-3 pipe length), if its long, you want an high pressurized pipe so it travels fast to the end and doesnt clog in the middle
