Operating an external tuner on one slice and internal tuner on a second.

I have a remotely operated 6400 with internal tuner & SSDR 2.9.1 Current antenna is a B&W 90' folded dipole. I plan to add a zero five 10--80 vertical ground plane to the mix. The flex internal tuner is specked at 3:1, Zero Five recommends a 5:1 for their vertical. Thus, I plan on a remote coupler at the antenna base. such as the MFJ998RT. I figure if I assign the vertical to slice B and select bypass by deselecting ATU on each band it will allow safe operation of the remote tuner while maintaining my regular operations on slice A with the folded dipole. That said I expect pressing Tune with the ATU in bypass the remote couple should tune and not affect the internal FLX tuner.

Does this sound correct?

Thanks Steve AG4SO