I have just installed a new bathroom and am disappointed by the low pressure in the stall shower. Wondering what might be wrong. There does not appear to be any clog or low flow device in the shower head.

-- I have a private well with pressure tank
-- Shower is approx 28 vertical feet from the well tank in my basement.
-- Pex home run to manifold 1/2 inch to bathroom
-- Mixing valve is Rohl HY19BO
-- 1/2 copper from mixing valve to shower head and hand shower (have a shut off for each - and we have low pressure even when just one is in use)