Threshold is poorly written. What you're seeing (or not seeing) is the result of two problems.   The first, as Thomas mentions, is the screen it draws is too large. On other video game systems the video chip is in charge of drawing the screen. This is not true on the Atari - the game itself is in charge of drawing the screen. Because of that, it's possible for the Atari to output too many or too few scanlines. You can see this if you run it in Stella and hit either COMMAND-L (Mac) or ALT-
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