I came from a coastal town where we have 3 small islands almost exactly 30km away from coast, and we used to take boat rides to that island. In a way we have learned to judge approximate distance while at sea, using horizon line as a guide.
From the fourth photo posted by Yusheng above, the destroyers and frigates are around 15 to 25km away from USN destroyer as they are at the end of the ocean horizon, while Liaoning is closer, at about 10 to 15 km away.
By yesterday noon, Liaoning carrier battle group had passed through the international channel between Xisha Islands and the Zhongsha Islands, and continued to go down south. There are a large number of aircraft providing cover from Yongxing Island Airport in Xisha.