Will an object on the dashboard of a car slide more...?

First question: If it's against the windshield, it can't slide forward, so it can slide only backwards, which occurs when the car accelerates.

for your second question, "I believe since air resistance is negligible and since it is shielded by the windshield the box should not slide enough to determine a difference."

that makes little sense, air resistance is not a factor. The object is free to slide backwards, but not forwards. Whether or not it will actually move depends on the coefficients of friction between the object and the dashboard and the magnitude of the acceleration.

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The wording is ambiguous. What is the object? What kind of "box" is it? Is it upright or flat? Is it positioned equidistantly from the maximum range? What other factors could affect this object? What kind of windshield are we talking about?