The calculated distance (air line) between Hà Tĩnh and That Phanom is approximately 125 miles respectively 201 kilometers.
By car or train, the actual journey to That Phanom is certainly longer, as only the direct route (as the crow flies) between Hà Tĩnh and That Phanom has been calculated here.
Air line (approximately)
201 kilometers
109 nautical miles