Prompted by a suggestion that a different orientation of the water shock / anti-surge accumulator would be better for this setup I took the time to rearrange the hoses for the accumulator and the nozzle supply.

The new orientation of the accumulator off of the tee has the fluid exiting the pump proceeding directly toward the accumulator, and then veering off 90 degrees to go to the nozzles.

A log with this new orientation is shown below:

Overlaying the two accumulator orientations leads to the chart below:

The difference around 3000 rpm is almost certain to be related to the manner in which boost built during the two sessions, rather than a result of the different orientation.

It is hard to discern if there has been any change to the quality characteristics of the flow with the change to the placement of the anti-surge accumulator; but there has not been any detrimental effects from the change so I plan to leave the accumulator in the new location.