sounds like it's somewhere in your margin settings - most apps (if not all) get teh paper dimensions from the printer driver usually this is a printable area and the whole paper size. If you then tell the app to resize in any way, it does it within these constraints. Could be that the app is adding margins. Couls also be that the app needs to resize this way to maintain the page format. You need to check it through, starting with the printer settings for that paper size.
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