0.9mm nozzle is it to big

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my water injection is set up on a vehicle running 1.5 bar overboost and holding 1.25 bar, ihave been told i have a 0.9mm nozzle ie black/white ring, how do i work out this is the correct size or if anuyone could guide me as to which would be the best size
its used to charge the inlet charge so nozzle is located just after the intercooler exit
also can 2 nozzles be used togethe ie one for charge cooling and the other for piston crwon cooling by locating the jet in the tophat the top hat is found above the throttle body on my turbo engine