I drove fire engines so I should remember this stuff. I do not. Getting old. Non laminar flow? I think there may be a formula expressing this. The larger the pipe the less the effect. An example: large water pipes or water mains, when they reach a critical large diameter create a mind of their own and flow high rates fairly independent upon the size and pressure. Smaller pipes tend to be more non laminar. More turbulent. Ratio of surface area to volume?
Rather than the larger the cross section it is the closer the flow rate is to the maximum capacity of the total volume including the frictional loses in the turns of the pipe. Square pipes tend to have maximum flow rates near the center as they reach the maximum flow rates. This usually is a round. In rectangular pipes it is more ovular. But turns especially near the entrance and exit have more effect than near the center of the length.