The DFD finisher might require a delay in the output flow to be able to process the output of the printer. To understand the impact of this delay on the productivity of the printer and thus on the combination printer + finishing line you need to take into account the way the printer handles this request for this delay.
Based on this observation, printers can be split into two categories:
Printers with a variable time between images positions. When additional time is required, the scheduler extends the internal time between the image positions to create the required time gap. This increases the time between sheets at the output and reduces the output in an (almost) linear way.
All Canon print engines with a DFD-interface, with the exception of the VP-i-series and iX-series behave this way.
Printers with a fixed image position. These printers internally use a fix slot per image. When additional time is required the scheduler will increase the number of slots used and add empty slots to create the required time gap. The delay is always a multiple of the interval time. This will reduce the output in a stepwise way.
The vP-i-series and iX-series schedules in this way.