With an Aftershock head, I would guess maybe 20 degrees above the air temp. With a Rand and most other's, I would guess pretty close to the 210 you are seeing.
Thermosyphon requires a narrow passage for the water. Otherwise, the water will just roll within itself. So heads with large open cavities, the water just rolls around in the head. The heat will slowly climb both hoses until it gets to the top of the radiator through the hose that connects there. When the hot water hits the top of the radiator tubes, it will kick in the thermosyphon in a big way. The cold water in the radiator will dump into the head forcing the hot water in the head into the radiator. After the initial dump, flow will drop off and even out.
The Aftershock head with fins around the combustion chamber induces thermosyphon between them right away. Water flow starts slow and speeds up as temps rise.