Huh, that's odd. I did a rescan with my Panasonic and didn't pick it up. The tuner in the Panasonic isn't the best though.
Just tried a scan with my Sanyo TV and that didn't pick it up either, so I don't know what's up with the 20.4 you're picking up.
I'm way up in the very northeastern tip of CT (Danielson) , 50 miles and 2 edge from the Waterbury transmitter with 88% signal.
It does look like there's a bit of tropospheric ducting going on here, 9 and 5 are coming in perfect here tonight, usually they're a no show. Maybe it's got something to do with that.