[PzLdr]

Their war plan called for an invasion of Germany, and a march on Berlin. One of the reasons they were deployed so far forward [coupled with the unrealistic belief they could hold their entire border].

BAD miscalculation. Germany had them surrounded on three sides [the U.S.S.R had the fourth], and except for the mountains in southwest Poland, the Poles had no readily defensible geography before the Vistula and Narew Rivers. The Germans were able to execute a concentric double envelopment.

[lizol]

Their war plan called for an invasion of Germany, and a march on Berlin. One of the reasons they were deployed so far forward [coupled with the unrealistic belief they could hold their entire border].

Not exactly.
Poland's war plans were based on the military alliance between Poland and France and Great Britain.
And - if the allies actually respected the alliance - the war probably would have looked much different.

As to "the unrealistic belief they could hold their entire border" - Polish commanders were fully aware of the fact, that it would be impossible, and they considered building the line of defense inside the country.
The problem was, that there was a big risk, that the German troops will enter Polish territory, reach the line of German border of 1914, and stop there.
In such a case - you know - Chamberlain would have probably announced happily the next "Peace for our time" - paid with the price of large part of Polish territory (without any resistance from the Polish Army).