Found these two articles while looking for info about balancing flow between CIS injectors.
Think this puts some good info about why balanced flow is important and what those extra allen heads do next to each fuel line on top of the fuel distributor.
Adjusting CIS flow with new injectors. (this may no be necessary under normal conditions - may be necessary if previous owners have messed with those allen head screws)
Importance of clean injectors, How uneven flow messes with mixture.