Thanks jimjim1
The corridors should be along a large circle of radius 4840 km (as measured on the Earth's surface) centred on a point on the equator at 64 degrees east.
This is the point below the INMARSAT IOR which has been doing the receiving of pings.
I have not been able to draw postable diagrams yet these are close to yours.
The explanation for this is spread over several pages of previous posts by myself and several others especially including a photo of a map from the SAR authorities.