Why twilight is shortened near the tropics

The Sun which follows the Earths curving magnetic field drops away at the tropical boundaries of Cancer and Capricorn. Obviously, we get a Sun image in the tropics coming in from either the north side or the south side, but the Sun rises quickly and sets quickly due to the Earth's magnetic field diverging away as it hits the dielectric zone of the tropics/low pressure zone. This is where the magnetic field diverges the most on Earth, and why the Globe theory comedy tells us Earth is wider at this point (oblate, lol)