"I'm performing a cash to Roth 60-day rollover (bound by the 12-month limitation)."
No, the deposit into the Roth IRA of the $9,600 withheld for taxes from the traditional IRA distribution is still a Roth conversion, no rollover frequency limitation involved. The fact that cash is distributed from the traditional IRA (effectively to you in the form of tax withholding credited to you) and you subsequently deposit an equal amount of cash into a Roth IRA does not change the nature of the transaction from being a Roth conversion. It is neither a rollover from a traditional IRA to a traditional IRA nor a rollover from a Roth IRA to a Roth IRA which are the only types of rollovers that involve this limitation.
If you rolled over to a traditional IRA any of the $9,600 withheld for taxes, that would involve the limitation since it would be traditional IRA to traditional IRA.
Section 408A(e) of the tax code includes:
For purposes of section 408(d)(3)(B), there shall be disregarded any qualified rollover contribution from an individual retirement plan (other than a Roth IRA) to a Roth IRA.
Section 408(d)(3)(b) is the rollover frequency limitation. A "qualified rollover contribution from an individual retirement plan (other than a Roth IRA) to a Roth IRA" is the definition of a Roth conversion.
