[Jerry Clayton]

The reason is-----the point of closest contact is not at tdc or max valve opening---it is a few degrees before tdc as the exhaust valve opens and a few degrees after tdc as the intake opens---the piston is chasing the exhaust valve as it closes and the intake valve is chasing the piston as the piston starts down

A little rocker ratio change really doesn't amount to much at those points so unless you are really near the limits you will probably be ok, but I would check anyway