How do Iran's 7 islands form an 'arch defence' helping it monitor Strait of Hormuz?

Iran has a network of seven islands along its southern coastline, with researchers calling it an "arch defence". The islands - Abu Musa, Greater Tunb, Lesser Tunb, Hengam, Qeshm, Larak and Hormuz - allow Iran to monitor the Strait of Hormuz. Reportedly, the Larak island has Russian-made communications-jamming systems, making it easier for Iran to regulate ship traffic.