With regard to the “reason” for the distribution, you would select RMD if available, but otherwise separation from service which normally opens up the entire balance for distribution. However, some plans might restrict partial distributions so if no RMD reason shows, I would use separation from service and add RMD to that reason.
If you wanted to do a direct rollover to an IRA, the plan would have to distribute the RMD before rolling over the balance or at the same time as the direct rollover.
Note that for the year you reach 70.5 you have the option of deferring all or part of that RMD to 4/1 of the following year, but if you do that you will have two taxable RMDs in that second year. Deferring is not beneficial in most cases, but there are few taxable income situations when it is beneficial.
Finally, the call center might be confused by the numerator/denominator terminology you are using. While that is what it is, the usual figures are described as the account balance and the RMD divisor. As for the reps, you might ask to speak to a senior staffer, and if you are persistent enough you might get transferred there.