The Osprey author (Charles Stephenson) lists 24 works in his bibliography and one website, but most pertain to the island's earlier years, and none of them would appear to be the source of the radar network shown in his "radar map". I checked the most likely source book -- the Shores/Cull book "The Hurricane Years 1940-1941 -- but it doesn't even mention radar (!). Stephenson lists five of the pre-February 1942 radar sites which are shown on his map: three are along the SW shoreline (at Dingli and Ghar Lapsi); one is in the NE at Madliena, and one in the south, at Tas Silg. One more is shown on Gozo. They all apparently had 360 degree coverage. None of these sites are remotely near Delimara or Kalafrana, however, nor are they near Ft St George or Ft Tigne. Possibly these might have been the locations of post-February sites?
It's obvious from the North arrow on the two recon photos that the original imagery analysts knew where they were, as the arrows would be incorrectly aligned for Delimara or Kalafrana. So, I assume that either Arena or his source for these two photos got a little mixed up. Hard to say what is in those circles, however; they certainly don't look like wartime British radar set-ups.
While Sicily was only 60 miles distant, the air miles to Malta could be several times that from Sicily's more distant bases -- and the air raids seldom flew a direct course (they'd prefer to approach from the south, in order to return home by the most direct route). The Malta-based radars could detect airborne targets at up to 50 miles, giving the defenders a limited, but useful period to alert their AA gunners, scramble fighters, and -- equally importantly -- give personnel and civilians an opportunity to seek shelter.
I haven't read anything about the Brits' tactical radio intercept capabilities on Malta, but this could have given them long-range air raid warning, too. The Germans made excellent use of this capability during the US daylight air offensive against the Reich, for instance. As the bombers would take off and laboriously form up over England, their transmissions would be detected long before they were in radar range, giving the Luftwaffe ample time to assess their numbers.
Bruce