No - you cannot use a printed sheet.
Turns out printer ink is a dye - and does NOT affect the reflectance of the paper. 940nm light goes right though dyes.
You need paint.
The best way to go, is to use spray paint. Dark gray should do it. On cardboard. At least 3 coats.
A white sheet of paper is 88% reflective.
A bit of cardboard is about 50%. Your hand is also about 50%.
The blackest flat black spray paint is 5% reflective.
So to approximate 17%, you need a dark gray paint.
The calibration does NOT have to be exactly 17%.
A reasonably dark gray paint should be just fine.
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