I taught this stuff back in the 80s and 90s.
The first load coil was constructed by Oliver Wheatstone in the late 1800s. He really didn't understand why it did what it does. The load coil is an inductor. Because of cable pair capacitance and self induction, voice transmission degrades as distance increases. The load coil effectively cancels the self inductance of the cable pair which in turn increases the voice band transmission distance. The load coil, being an inductor or more commonly a band pass filter, is designed for voice band frequencies. A load coil in that specific bandwidth has an effect of 3,000 feet on both sides of the coil. Thus, the first load coil is placed 3,000 feet from the office and the second is placed 9,000 feet from the office, which places the second coil 6,000 feet from the first. Subsequent coils are placed 6,000 feet apart. But the loading of a cable is not needed on phones less than 18,000 feet from the office. Beyond 18 KFt the cable pair is loaded. No phone shall be located beyond 3,000 feet from the last load coil. Another load coil must be installed. Load coils have no effect on power influence.
AC induction/power influence is a problem on long runs. Cable placement is important, but across the road does not always help. I remember my group chased a power induction problem in El Paso several years ago. An 1,800 pair exchange cable had "ground hum" on every pair. It was in conduit for a few miles, then broke off into buried and aerial. Engineering department fought this problem for several months, then contacted the power company. After another few months the power company found an unbalanced primary (27,00 KV) transformer on the other side of town. No one could ever explain it.
I've been out of the loop since 2000 so I don't know what a smart coil is. The last thing I taught is fiber optic multiplexers.