The overload doesn't necessarily have to come from the signal you're intending to receive. It could be any transmission.
I used to live a couple miles from a hospital that apparently had its own paging system (or just happened to have a commercial one located very close by). If I was using the Scout to reaction tune the scanner it would tune to the paging system frequency every time someone got paged. And this in the RF jungle that is Los Angeles. For that signal to have punched through it had to be something like ten times stronger than all the other RF energy combined. Considering all the other broadcast towers within five miles, that had to have been one REALLY strong paging transmitter. Something like that would clearly cause overload in a receiver sensitive to it. But it would only cause a problem when someone was getting paged.
EXACTLY!
I monitor a nearby county's SO and the transmitter is in the 40-50 mile range. It is a VHF-High frequency, and is obviously very distant and weak. With attenuation OFF I get NOTHING. With attenuation ON it comes in with two bars on average.
So even though it is a "distant" signal, without attenuation I don't get as much signal through as I do WITH attenuation, because of an intense amount of RF energy in that band, near my location, NOT near the site I am trying to pick up.
The way attenuation works in different bands is a VERY funny thing, and combining that factor with antenna and coax factors makes things very interesting.
I am a persistent type, so I look at it in the following way.
There is almost always a way to hear what you want, you just have to try different things and be creative. It is almost NEVER the scanner that makes the difference, it is usually your antenna setup and settings.
Back before the days of wonderful forums like this one, there was no way to share so much information and so many tips. When I first started it was trial and error for the most part.
As Bill Cheek said, "I would rather have a cheap scanner with a great antenna than a great scanner with a a lousy antenna". It usually comes down to your setup...