Poland lies directly under the great circle route from the Middle East (Tehran) to the US East Coast (Washington, DC).
"It would be the first American strategic missile defence site outside U.S. territory, and would be designed to defend all of Europe against intercontinental-range missiles - primarily those launched from the Middle East."
I think you are missing the strategy here.
Nice map. And why it would be better to intercept the missile over Poland than near Main?
Poland lies directly under the great circle route from the Middle East (Tehran) to the US East Coast (Washington, DC).==
This route is deficient from point of energy. Who wants to launch against Earth spin? They would launch rather over north pole in order don't have earth spin worked against it.