the signal emanates from the coil goes over the top of the antenna and outward. a "stick" antenna emanates from the bottom of the antenna and out over the top. with the center load the signal will travel farther than the "stick" will.
the SWR of the antenna is how close the signal passes to the top of the antenna, too high or too low gives a standing wave over acceptable limits sending the signal back into the antenna. your body affects the SRW, getting the coil higher gives a cleaner path for the signal.
center coils are much better.
This is simply not true.
First, regarding the loading coil:
The entire antenna radiates, not just the coil itself. The purpose of the coil is to make the antenna
electrically longer while allowing it to remain physically short.
The purpose of placing the coil at the antenna's midpoint has to do with the amount of distributed capacitance along the length of the physical radiator. In short: The higher up (to a point...), the less capacitive reactance must be cancelled out...and the broader the antenna's 2:1 SWR bandwidth will be.
Next, SWR:
Standing-wave ratio is a measurement of how much energy is reflected back to the transmitter (source) as the result of an impedance mismatch at the antenna (load). Standing waves do not "come off the top of the antenna". They are, however, present on the transmission line (coax) in the event of a mismatch.