that is not the way the W-4's work anymore. The whole idea of exemptions doesn't exist on the W-4 form.
if you want more withheld, so that the refund is greater at the end of the year, simply check the 'single' box on the form and that is all. Even you want even more withheld, place the amount you want withheld on line 4c.
https://www.irs.gov/pub/irs-pdf/fw4.pdf
is it a good idea to withhold money as a form of forced savings? personally, no, the IRS doesn't pay interest and the banks do!