Just seems like an excessive amount of power in use for going from South Korea to North Korea; or even to Japan for that matter. Seat of the pants estimate- maybe 100-250 kw Transmitters or so it sounds like to me. I'm somewhat familiar with the sound of Radio South Korea- power levels sound comparable to me; again nothing factual, just a rough guestimate
If your receive target is using a small, inconspicuous, run-of-the-mill portable commercial SW receiver with a whip antenna there is no such thing as too much power. And if you look in that frequency region you will see many BC transmissions from North and South Korea, aimed at each other or the general region, running powers from 50 to 250 kW. When the Voice of Hope, The Voice of The People, or KCBS Pyongyang transmits in Korean it is not meant for anyplace else, but those are the power levels they use.
However, one has to be careful with relative or received power levels, they can be very deceiving, especially on HF. For example, day-to-day variations can make a huge difference, but seasonal variations are even larger.
It is essentially impossible to tell an HF skywave 100 kW station from a 200 kW station using relative spot checks performed at different times, you simply can not pin down a skywave received power on HF to within 3 or 6 dB without some significant effort, they are far too up and down on average. And 6 dB is the difference between a 200 kW station and a 50 kW station. When we work in microwave, with direct line of site and practically no propagation variation we generally consider the error of measurement for any single measurement to be +/- 2 dB (unless on an instrumented range), and HF skywave is much worse than that.
This morning I did a direct comparison, for what it is worth. One of the nice things about an SDR is that it can display a wide range of freqs simultaneously, and record them for review, making simultaneous measurements easy. Using a 150 kHz bandwidth and starting at 1500 UTC and for the duration of the V24 transmission I recorded both V24 on 6215 kHz and KCBS out of Pyongyang DPRK on 6100 kHz in a single file, from a single antenna, pretty much making all variables on my end identical. The two stations are close enough in frequency that propagation differences (other than instantaneous) should be negligible.
KCBS Pyongyang is listed with a transmitter power of 125 kW and a non-directional antenna.
V24 on 6215 kHz was peaking at a level of –54 dBm (S9 +19 dB), with occasional fades down 20 to 30 dB from that. KCBS on 6100 kHz was peaking at about –48 dBm (S9 +25 dB), also with fades 20 or 30 dB down from the peaks. On average I would say KCBS showed MORE fading than V24, but not deeper fading, and KCBS consistently showed a higher peak. The signal level differences between these stations were indistinguishable by ear, in fact, if anything, the V24 sounded slightly stronger, with the female voice (KCBS was mostly music and male announcer) punching through better.
On the surface this data would suggest that, disregarding transmit antenna patterns, KCBS is transmitting 6 dB more power than V24. We know KCBS is at 125 kW. 6 dB down from that would be 31.25 kW. It would be easy to draw a possible conclusion that if both stations are using non-directional antennas and KCBS is at their published 125 kW, then V24 must be about 30 kW.
However, I would be very leery of making any conclusion from one set of measurements, no matter how hard a person tries to keep it an apples and apples kind of thing. For example, what if V24 is running 250 kW, but with a directional antenna and I happen to be in a null, a sidelobe, or just on the edge of the main beam, that is 10 dB down? That would produce pretty much the same results.
Now, if three or more people did the same test, synchronized but from geographically disperse areas, all yielding the same or similar results, then I would start to say V24 was at 25 or 30 kW. But I am not sure there are three or more people even looking at V24 on a given day.
I do think plotting points on a projection or the like is a valid technique and given enough observations from enough locations I would expect patterns and usefull inferences to emerge after taking into account propagation conditions which could tend to temporarily change the typical signal path direction and even enhance or attenuate signal strength. This is a complex process, with a lot of variables, and is frequency dependent. Someone with Antenna and Propagation Modeling could have fun with this. I'm just a Hobbyiest and don't have that kind of expertise- but do find this interesting.
If you can take the propagation for each individual intercept and the individual receive station variations (such as what receive antenna was used, its orientation, what feedline was used, what was the performance limitation of each receive station) into account then plotting reception to determine a possible radiation pattern might be valid.
Merely saying the signal was received by station X at S7, Y at S5, and Z at 20 over S9, while station R did not receive it at all, or worse yet, no signal levels, just it was received by X, Y, and Z, but not R, tells you nothing, even if you know the locations of each station. Factoring in the propagation for each specific and individual reception by each station starts to narrow it down, but still leaves the individual receive station performance factors in question.
If you have large enough pool of individual receive stations, and you have reports from those stations on other signals of interest, then maybe performance differences might start to average out and be less important. You could identify the “flyers”, the stations that are always reporting everything as 40 over S9 could be identified, as could the stations that struggle to hear what should be power house signals.