Okay hustle up. Looks like I figured out the proper conditions to have the pedestal available for Reginald.
When I arrived at Corvo Bianco to fight the Bruxa, there was a vase on that pedestal. I moved on with the story until I fought Dettlaff. Then when I was free to roam, I immediately did the Reginald quest.
When I returned to Corvo Bianco and met with B.B., the pedestal was then empty. I even tried to complete all renovations at Corvo Bianco by hastily medidating then fast traveled to multiple regions, and still the pedestal remained vacant.
Looks like the requirement is to be able to have the Reginald figurine prior to your arrival at Corvo Bianco as the owner of the estate.
To verify, I reloaded an earlier save. Just before looking for Milton at the palace gardens, I fast traveled back to Corvo Bianco to meet with B.B., and when I got there, the pedestal has a vase.
I am gonna try again to obtain the figurine after meeting with B.B. and see if the pedestal becomes empty.
Btw, I am playing NG+ at level 92.