What we come up against when setting up an AM transmitter and antenna under the part 15 rules is that the allowed antenna length of 3-meters is drastically short at medium wave frequencies, thus cutting down significantly on achievable transmission range. But the trick of using a loading coil can make a 3-meter antenna think it is actually longer. Here is a video that neatly explains how a loading coil does what it does:
Carl Oliver's Loading Coil Demonstration
Great demo! That's why when the 3 meter rule was made way back when, it was not figured that people would use this to get the short antenna to work like a longer one. The large coil in the Procaster is the loading coil and adding length to the antenna would just make it worse not better as you'd have to change the coil also.
Capacitance hat makes a massive difference, though not radiating. I spent part of yesterday working up on my tower. There's more to do still ...and it can wait a bit.
1640 am antenna in Virginia.....WAQM . He had a good signal from this antenna....Except his signal was not going the direction he wanted....It followed the salt water. I could here his station 5 miles away ...Loud and clear. His station also past fcc inspection...Stupid neighbor turned him in twice. The antenna had a capacitance hat and that really opened things up.
Diablo has gotten me interested in looking at the 'top hat' for part 15 AM. In the past some people have spoken highly of top hats while a few have said that it does very little. I personally never bothered to find out until now. According to this link at Wikipedia this type antenna is also called a T-antenna, flat-top, or capacitance antenna.
https://www.onallbands.com/what-is-an-antenna-capacity-hat/
This refers to amateur radio use, but the theory is the same for Part 15 AM broadcast band use.