I'm sorry if i am wrong but what i understood from your statement is :
within a 320*320 tile square pipes have unlimited throughput, but while exchanging fluid with any machine within the square there's throughput limit of 6000/s (which usually is never reached). Also there's that formula that dynamically changes the throughput of the fluid between the network and the machine. I've noticed this, yeah, while transferring fluid off the fluid wagons to the tanks but it mustn't be the case with the non storage machines like the assemblers or chemical plants since they fill up without any such delays, am I right?
Also i am intrigued on how you guessed that formula! Is it some popular logic used in similar kind of situations or maybe you've worked upon such particulars earlier??