[satyrnein]

Actually, my plan was to have the recognition area expand beyond the visual size of the input box as soon as your pen touched the input box, so as not to penalize the user for wandering out of the box a bit, while not having any visually jarring effect, but it's worth experimenting.

And of course, there is still the option of scaling the page overall. It's possible the audiences that would want bigger input boxes would also want the text and images to be bigger as well, but it needs research to confirm.