If the engines’ satellite pings were being done once every hour, after the 4th ping (that followed the turning off of the plane’s transponders) there would be an addition hour of flight time before the 5th pinging engaged. So the possible flight radius can be increased by another hour’s flight distance. That brings the radius out to cover Afghanistan and a significant chunk of Iran.
There are a lot of “suitable” flat areas in the Iranian desert in which an experienced pilot could land. Just because the transponders were turned off doesn’t mean all the navigation instruments and equipment wasn’t functioning. The pilots could have entered some predetermined (and previously scouted) coordinates and flew the plane there to land and meet up with confederates awaiting them. This is definitely NOT beyond the realm of possibilities.
I am skeptical that this aircraft could be landed on a flat area in the desert. Her empty weight is ~145 tonnes, or over ten tonnes per wheel.