update; instead of using the shower outlet, i use the handwash faucet instead and convert to folding type as pic.. rm80 for the solution and solved the problem.. thanks all for helping

hi. how do u control the whether the water only goes to the top rain shower or hand shower? based on the pic below, the valve is a 3 position (top shower - off - hand shower)?
water outlet is from the top mounting point (with red arrow)? the ad says top supply but the pic looks like bottom supply (green arrow).
how do you adjust for clearance because the water supply pipe coming from inside the wall might varies in length?

shopee user review pic:
https://shopee.com.my/HUN-HRSS-906-Top-Inle...2440.2181115684


Another similar product:
https://shopee.com.my/Abagno-SPW-969-668-2-...2440.6571828704
Water supply at the top but the valve at the button. How does it control the top rain shower? Inside the big support tube, there's a small water tube that goes down, to the valve, and back to the top to the shower? 



I don't get it unless both top rain shower and hand shower are both operating together when the hand shower is used, which makes the pressure low.