I don't agree on a top had or coil at all for any antenna, unless you "have" to shorten the antenna, and/or it's needed to bring the antennas impedance down to 50 ohms. In reality, the most efficient antenna are ones with "no" extra components. Adding components are used to help "shortened" antennas operate almost as well as a full sized 1/4 wave antenna, while trying to add the least amount of loss as possible.. But why shorten and/or add these losses at all? Worse of all, why add these losses on a quarter wave!
Perhaps Jay with his Predator 10K would take his off as well, and make a true .64 straight antenna/radiator.. A capacity hat makes sense on the Ham bands, where you must shorten the antenna significantly, but for a quarter wave 27mhz antenna, this literally makes no sense.
Many don't get this fact, as W5LZ pointed out, a better antenna is one with no added inductors, capacitors, and/or top hats at all.. Yes top loading and/or a capacity hat may be better than a bottom fed coil because it adds lower losses if you "Must" shorten the antenna! However, the better solution is not to shorten the antenna at all, and not add this unnecessary losses. Generally a quarter wave doesn't need any components at all, as if the radials/ground plane kit is adequate, a flat SWR isn't a problem. The antenna would also be much more stealthy, by making it another foot or two taller, and getting rid of any extra crap on top.
A .64 or 5/8th wave needs an inductor to tune it. The antenna has capactive reactance that needs to be canceled out, and the coil adds to the antenna electrically, and once you get up to a 3/4th wave, the antenna's impedance is near 50-70 ohms. A 3/4th wave antenna just as a 1/4 wave needs not coil or capacity hat at all.
A end fed 1/2 wave antenna is actually more difficult to tune than either a 1/4 wave, 3/4 wave, and/or a half-wave, as it's impedance is well over 1000 ohms! You generally have to use both capacitor and inductor lump components at the antennas feed point, or a very efficieint impedance matching transformer.