You just modify the Control Points of the base surface!
Yes The base surface "modified" modifies Volumes surfaces etc... above it!

History is not automatically enabled on each function!
Here the not intuitive thing of the (mine) method is that you select the volume(s) "Flowed" one time!!! for enable the History! :)

And all after works like a charm!
You move the Points of the base surface, and all above are modified! :)
Many time during the session if you don't touch the letters & surface for other modifications...