I am a minimalist in water use and found using bypases that 4 jets need a certain pressure to operate, eg if you tilt the brush to the left or right, that the higher jets fail to deliver water if there is not enough flow or pressure or volume, maybe because the jet size doesnt balance with the water flow. Sounds basic I know, but it is !
Which two jets are not ejecting water ? and what sort of manifold are you using- got a pic anywhere online ?