The 96 value in those calculations is the maximum screen resolution (DPI) that will fit inside a "page" printed by JavaScript.  This is mainly because the browsers use the screen resolution, and not the image resolution to print by.

If you increase that number, you make more dots (pixels), but since the browser only allows a maximum of 96, you will still only fit 96 dots in one inch.  This causes the image to get larger than the paper.

At this time, I do not see any way to print at a higher DPI from within JavaScript.  This is a browser limitation.