No, that's wrong. The book always has to be under there, otherwise you aren't proving anything (or at least, the odds are worse). The idea is that your counter

No, that's wrong. The book always has to be under there, otherwise you aren't proving anything (or at least, the odds are worse). The idea is that your counterparty cannot ever ask for both the book under there and to see Waldo, so they never know where the book is. You can spin the book around under the cardboard to put it in arbitrary locations, therefore just seeing the Waldo doesn't help.