Im guessing no one want's to make the call incase it goes tits up... if the collets are not a snug fit around the valve stem they will start to stretch the grove in the valve stem the spring holds the retainer in place and the tapper in the retainer suits the collet extra diameter will mean the collet will sit higher in the retainer, I would doubt enough to make any real difference as long as the spring will maintain tension what Im wondering is the grove height the same between the two and can you use the vg30dett retainer , collets with the ca18 springs or perhaps see if jun retainers/collets are better suited . To pop you need the mechanical advantage of the spring to fail,eg float,piston hitting the valve or spring binding