The INMARSAT which must have been involved in the last hours of pinging communication must have been IOR which is geostationary above the equator at 64 degrees east. (This is the only INMARSAT which deals with ACARS comms which has coverage over the longitudes that the plane was in then).
As I have said before, there would be no triangulation, just (accurate) distance information gleaned from the time to negotiate a single ping (a few short messages backwards and forwards).
The announced northern corridor (N Thailand to Kaz/Tkm) tells us that the distance measured from the final (8:11am) pings was about 4550 km as measured on the earth's surface (to a spot below the satellite). That is how far those two ends of the corridor are from the spot.
So the possible 8:11am locations lie on a circle of that radius around that spot.
I will post a map shortly.
Interestingly, also on that circle, within the northern corridor is Hotan.