I am no physicist, so take the following with a large pinch of salt.
If fluid is entering the wide end at a given flow rate (in units of volume per unit of time) it must be exiting the narrow end at the same flow rate, or the nozzle would explode. So the flow rate will be the same at the entry and the exit, and indeed halfway along, or at any point along, the nozzle. Of course, the speed will increase between entry and exit.
The same will work in reverse, with fluid exiting the wide end at the same flow rate as it enters the narrow end, though in this case the fluid will slow down between entry and exit.
Assuming a fluid which is for practical purposes incompressible (a liquid rather than a gas), its mass will be directly proportional to its volume, so the mass flow rate will be the same all the way along the nozzle.
If (a big if) I am right, then the dimensions of the nozzle are immaterial.
Andy