Then imagine you could travel very fast at 100 feet off the ground, and you follow the direction in which the sun appears, i.e. keep its azimuth constant relative to your own position. To be clear, you have a sundial on board your aircraft and you make absolutely sure the shadow remains in exactly the same place.
You will end up in that place in the Congo.
What makes you think that following the rays of the sun would take you to that location? The sun's rays are always coming in from the East along the lines of latitude (from a side view).
Now imagine that you are sitting in your house on the shoreline of Miami, looking at the rising Equinox sun.
Suddenly, the entire earth disappears and you are floating in space. Luckily, you have a space suit on and a rocket booster pack. You follow the sun with your rocket boosters. Where does it take you? Does it take you to a location where the Congo used to be?
The shape of the earth has nothing to do with the bearing of the sun. Those lines you had made that curve Southwards might meet at a point and tell you where the sun is at its maximum overhead zenith above the earth, for all of the earth, but this is a very different concept of following Eastern lines that depict the sun's bearing.
The actual sun is very far away in RET, and so its bearing is very distant and not directly connected to the point on the earth you are talking about. That is just the area where the sun is directly overhead for the globe shape.