I just finished a shower remodel this week and the brand new no-name valve and 10" rainfall showerhead from Homary.com which advertises 1.8GPM is only delivering about 1.3GPM. I flushed the pipes before installing the showerhead, so I don't think there is any debris in there. Also I am getting nearly 1.6GPM out of the hand shower that is plumbed to the same valve. I measured the flow from the stop valves in the vanity sink which is on the same line and I am getting 4GPM there. Any suggestions on how to get more water or more velocity out of the rainfall shower head?