Having been a student of US frontier history in my earlier days, I must offer another version to the Scots-Irish migration within and into the US.  But I would offer first, though, that the Scots came to Ireland, not just because (if that at all) of hard times in their own country but at the invitation of the English who were anxious to tamp down the ferver of the natives in the northern most area of Ireland.  Coming directly to the mid-Atlantic region of the US, these Scots-Irish (having come from Scotland to Ireland to the US, without a drop of Irish blood between) moved into the Piedmont and mountain areas just a tad deeper in than the Germans later.  While you do have Scots coming down from Maine and Nova Scotia (as did mine), as well as Irish coming directly over from Ireland prior to the 1800s (again as did mine in the 1600s into Norfolk) the specifically designated Scots-Irish did not depend on a more northern landing before migrating down.

Katie Holland
Washington, DC