This question highlights a common point of confusion…
How do I determine if my process is pressure-limited using my machine’s pressure curve?
The pressure limited process will have a plateau on the pressure curve prior to transfer. This will also correspond with a drop in the velocity at the time of pressure limiting.
A good way to test this is to increase the maximum pressure, and see if the peak 1st stage pressure increases. If the peak pressure increases with an increase in maximum allowable pressure, then the process was pressure limited.
For more about this topic, please review: Providing a Buffer To Accommodate for Variation