Johor starts from the widest gap
Singapore's output per head is 8.8 times Johor's, the widest of the five pairs and slightly wider than Singapore–Batam. Part of this is geography: the figure covers the whole state, rural districts included, while Batam, Shenzhen and San Diego are city or county units. Johor Bahru district alone would show a narrower gap.
8.8× Johor · 8.3× Batam · 5.4× Tijuana · 2.0× Øresund · 1.9× Shenzhen