The two "corridors" are defined as follows.
Draw a circle on the earth with centre 64 degrees East on the equator and radius 4840 km as measured on the earth's surface.
(This is the 40 degree circle from satellite IOR).
Then erase those parts of the circle which are under the coverage of satellites POR (to the east) and AOR=E (to the West).
See coverage map here
http://www.inmarsat.com/wp-content/u...ember-2013.jpg
This will leave you with the two arcs marked red on the Malaysian map.