Any hot runner/manifold requies some melt pressure, to distribute the melt from the center of the mold out to the injection point(s). This is like an automotic transmission, it takes say 9 HP just to make the system run! I have seen times when the pressure loss was so great, a new manifold system had to be built because we knew we could never consistently fill the tool and achieve the quality/scrap rate required. Then I've seeen other molds that required replacement of drop(s), valve gate pins, and tip orifice and styles due to the same loss.
It sounds like you've never done this before, so here it is short and sweet. Inject through the nozzle and record the peak injection pressure. Now do the same thing but through the open mold, record the peak injection pressures. The differance is the 'pressure loss' of the hot runner. I expect you will be surprised to know how much pressure you are losing on good running molds!