I'm a heck of a lot closer to them than you are and it's always so-so here after dark. My guess is they change antenna patterns/drop power after dusk? The East Coast between Richmond and Boston is so densely populated, it wouldn't surprise me a bit.
We'd probably have an easier time hearing them in Bermuda and the Bahamas.
They are 50 KW day and night. Daytime antenna pattern is nondirectional but their nighttime antenna pattern has the main lobe directed east...
perhaps to protect KAAY Little Rock AR also on 1090.
As you suspect, they send a lot of signal towards the ocean... probably sounds like a "local" in Bermuda.

("local" in quotation marks because IIRC Bermuda has gone to all FM.)