You may have only one IRA theoretically, but SEPP calculations are done a bit differently. I try to stay on top of these issues specifically, and I love web-based articles or reference materials provided by the financial institutions/brokers that are written for the consumer, even if I follow that to the IRS or other resources.

And I don't think much has changed for this provision in all these years.

So, for example: https://www.thetaxadviser.com/issues/2008/oct/substantiallyequalperiodicpaymentsfromanira.html

"In the payment calculation it is not necessary to aggregate the account balances for all IRAs owned; only the balance of the IRA(s) from which the SEPP is drawn is considered. This gives some flexibility in adjusting the account balance by splitting or combining IRAs in advance to obtain the desired balance...  It is permissible, however, to include more than one IRA balance in the initial payment calculation. Distributions must then come from one or both of these accounts. If a taxpayer needs additional distributions, establishing a SEPP from another IRA account while simultaneously continuing an existing SEPP is not prohibited."

There is the provision for no penalty when the payment was modified (which includes eliminated) because the account balance has been exhausted, if the calculation method used resulted in the funds being used up. But moving the funds would cause the payments to stop because of that action (not because of computation used or account balance loss)..."when an IRA owner transferred funds out of the SEPP IRA into another IRA during the payment series and then attempted to reverse the transfer and restore the funds, this was considered a modification of the series and the 10% penalty was imposed.³⁶ In one recent case, the 10% penalty was imposed when a rollover into a SEPP IRA occurred three months before the end of the required five-year distribution period. This ruling was made despite the fact that the IRA owner had already received the final payment in the series at the time the rollover was deposited."