Conclusion; if you want to sail in a specific cabin, yet know you will book in another, inquiry the professionals first.

For this itinerary, OP could have booked one way, used miles, and perhaps received his upgrade. But due to his booking choice / fare class he can't upgrade using his desired path.

Conclusion; Well for me at least, I will always now consult this wonderful site for relevant data prior to booking any mileage/paid ticket that are desired to be altered/upgraded.

Good Luck OP