In my point of view, you want to locate your shop in Sheung Shui is not bad, because:
1) You can attact a group of "Free Walkers" from China ( I always see they buy a lot at any shops in Sheung Shui).
2) Mothers in HK always order from web-site. They only purchase from the cheapest one amoung their web-site shop list every time after compare prices. If prices are the same, they'd see which one can offer more "Jet-so", such as free diaper offer is better than free wet tissue because the later one is cheaper.
Price is the most important factor amoung all.