Thanks to all who replied. The only information I could find on filter
specs, which I'm really curious about now, is from DXing.com's website
regarding two other Panasonic portables of the time. The specs for
those a

RF-2600 6 and 4 kHz
RF-2800 5 and 3.4 kHz

I've never used either of these two radios, but I have to think that
the 2200 is more likely to be the same as the 2600 as far as bandwidth
goes. The wide is fine for general program listening when there's
little interference, but when it's needed the narrow doesn't usually
come to the rescue. If the 2200 does use tuned circuits then it would
be best to accept it as it is and be happy with what it does do well,
and get a desktop for the tougher signals.