[ventus45]

So, when you look at Penang Island, you notice something very interesting.

The vertical yellow line is north - south, on the eastern side of the island. The butterworth PSR is top right. The red and light green lines through the yellow line, going south west from the radar, are the "look angles" for the "white circle".

Penang Island Terrain Masking - 1 crop75.gif Size: 365.76 KB  Downloads: 92

Penang Island Terrain Masking - 2 crop75.gif Size: 370.19 KB  Downloads: 90

Penang Island Terrain Masking - 3 crop75.gif Size: 393.62 KB  Downloads: 91

So, as the aircraft flew past Penang, to the south west, (NOT to the north west) the azimuth to it from the Butterworth PSR was rotating clockwise, slowly.

It was not until approaching the coast of Sumartra that the aircraft entered the "terrain masking" sector (the RIGHT HAND SIDE of the RED ovals around the mountain in the "profiles", and the lime green line from the radar head on the map plot), at about the 200 odd metre elevation level, say 220 metres, or about 700 feet AMSL.

As the aircraft continued to fly south west, it was masked by the range, until it flew out of the mask (the red line on the map plot). It was also further away, past Medan by that point. As it continued to fly south west, the azimuth from Butterworth changed only slowly, and the aircraft remained visible, until "cut off" at 200 Nautical Miles by the "low terrain horizon", a little outside of (to the left side) of the red ovals.

I will entertain CONVINCING Arguments to the contrary, only if backed up by very high quality geo-referenced data.