Clone clutch driver question

Im switching from flathead to clone. I hear that a common advice that goes like , if you used a 13t driver on a flatty , use a 14t driver with your clone at the same given track. In other words, increase your clutch driver by 1 tooth on your clone vs. a flathead . Anyone know the reasoning here ?
The clones dont turn as much rpm in stock form as the flatheads do, therefore you need the bigger clutch driver with the clone to get you more rpms. Im sure there are guys that dont go by the rule of thumb your saying, that there are some who use whatever gear ratio is the fastest for them no matter what engine they have on, and adjust accordingly for RPM and track conditions.