[IRCA] When is maximum D-layer absorption?

[Stephen Airy <pianoplayer88key@xxxxxxxxx>]

... so that absolutely NO skywave is possible on the AM BCB?
 
For example, let's say a signal on 1700 kHz is strong enough (as the skywave reaches the lower limit of the D-layer for its first hop) to spontaneously inflict severe enough RF burns to require immediate advanced medical intervention for survival.  At approximately what time of the day, year, solar cycle would it be absolutely impossible to detect any trace of that QRSS CW, PSK5 or other efficient-mode signal, no matter WHAT sophisticated radio + antenna setup you're using in an area at least 12,000 miles from the nearest power grid or thunderstorm activity?  Or if it never absorbs that much, how close does it get and when?
 
I've sometimes noticed traces of mid morning/afternoon skywave (at least 3 hours after sunrise / 3 hours before sunset) using my portable radio and loop antenna even in March/April and September/October or thereabouts.  I've especially noticed this with 1670 KHPY fading in and out, sometimes even within a couple hours of noon and within a couple months of the summer solstice.  Considering that I'd guess a sophisticated receiver+antenna setup is probably at least 100-120 dB more sensitive than my PL-606 and Select-A-Tenna, I wonder if they can get skywave all day even in summer (even if it's extremely weak)?
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