<DISCLAIMER> My knowledge about FT-8 is very limited. I once was a member of a small team operating as TO5M from FP, Saint Pierre & Miquelon. My teammates showed me which button to push now and then to keep the program going. So i sat there for a few hours and watched the contacts coming in , filling the logbook. I haven't worked FT-8 from home (not beyond a few test-qso's). <DISCLAIMER>
While i agree with Ernst, PA1EJO, for the most part of his mentioned article, i disagree that FT-8 is a low power mode. If you need the extra 10dB to make a contact on shortwave, why not crank up the power to a kilowatt? Just set everything right to put out a clean signal, or - at least - try do do so. On satellite, you usually have a dish to add the missing dBs to your signal.
No, it is a LOW SIGNAL Mode.
Now that i said that, i really don't understand why most of the FT-8 signals i can see on the satellite are beacon level or even above. There is no real reason for that. Correct me if i'm wrong.
I suspect many FT-8 users on QO-100 just can not monitor their signal because they can not receive while they transmit. They will never know they triggered Leila, because their transmit cycle is longer than the warning signal coming from Leila. Even if they hear or see Leila, most people on QO-100 think "some 1D10T triggered Leila, but not me". <polemic on>This also applies to many SSBers.<polemic off>
There is spectral density, dB/Hz, and this is with low power a high number because of the bandwidth of the FSK signal. Price to pay is that you need time to convey the message.