Ex RAF, in Chapter 28 of Sharkey's book, he indicates that the plan for 5 June was for Invincible to proceed in darkness to the south of the Southern tip of West Falkland and launch a Sea Harrier CAP as close to 80 miles of the coast of Argentina to "virtually challenge the enemy fighters to come out and play". The plan was for 3 harriers to launch in intervals to maintain a single ship CAP. There had also been intelligence that Argentine C-130's were still doing supply runs under the cover of darkness. Sharkey complained abut SAR coverage and reduced the station to 120 miles from the ship. Sharkey was the first to launch and said he could clearly see the coastline on his radar, and exhaust plumes from plants on the shore. The third aircraft was recalled early as fog set in. After the final recovery the 3 ships sprinted back east. Reference: Ward, Sea Harrier over the Falklands, pages 249-252
Well, it looks like around 350 nm from the nearest Argentine mainland airbase...
(From Invincible´s War Diary - and to avoid any comment, yes, I´ve stole it from Adm. Woodward´s safe)