Injector pressure differential

hi guys

so when tuning my brothers car everything was fine up to about 20psi of boost up around 25-27psi looking back over the logs I’ve noticed the fuel press diff starts to drop off now we have put a new holly dominator 2 stage pump in it before the dyno just to be sure. The other thing I’ve notice is once the bost is up around 25-27psi the battery volts drop from 13.5 to 13.1 do you think that’s enough to cause a volt drop issure with the pump causing the pressure to start to drop sorry in advance probably not enough info

Car is running a 13bt with 6 injector on e85