I've found that the term "mid-Atlantic states" is often confusing, even to long-time inhabitants. Several times this past winter, the National Weather Service referred to storms which would primarily impact the northern or the southern mid-Atlantic and I had to ask myself, "Where are we?"
I had always thought of the Washington area as the middle or southern mid-Atlantic, with the northern extremity stretching perhaps to New York City and the southern limit to southern Va. A number of dictionary definitions, however, refer to the mid-Atlantic as NY, Pa, NJ, Md., De., and Va. In other words, northern NY, on the Canadian border, is technically part of the mid-Atlantic. Other definitions sometimes include WV, the 3 southern New England states of Ct, RI, and Ma., and even the Carolinas.
You might be surprised to learn that for U.S. Census purposes, the mid-Atlantic ONLY includes New York, Pennsylvania, and New Jersey. I would say, therefore, that the term "mid-Atlantic" is as much a matter of geography as it is of climate, economics, dialect, and yes, state of mind.