Do you have any sense of how the signal strength numbers on a receiver correlate with your power level numbers?
There is so much noise [power] coming out of the LNB, that power levels are almost meaningless. Signal to noise [or carrier to noise] ratio is everything.
They don't, except that at a certain point the power level becomes too low for the receivers, and thus drop those numbers. Power level is how "loud" the signal is, the receivers numbers are how "clear" the signal is.
An LNB not even mounted to a dish has measured -30 dBm.
The receiver signal screens are related to bit error rates, which are related to the SNR/CNR, and not power levels. If power level had any affect, receivers on shorter coax would read higher than those on long coax.
When the levels drop so low that the SNR/CNR is reduced, then the receiver will show a drop.
The AIM will fail for power at the LNB when the levels are around -40 dBm, and the SNR is good.
Programing the AIM to measure at the receiver, lowers this level to -60 dBm, as this is very close to the minimum the receiver needs to have a good SNB/CNR.
"Rainfade" drops the SNR/CNR at the LNB, so the AIM is very critical of the SNR to pass the IV test. This is to ensure the alignment is done well.