Whenever a vigorous growing shoot is broken the auxin dominance is no longer there so there will be auxin dominance somehwere else.
So learning about auxin and how the shoot grows will help to make better decisions when it comes to pruning.
"Science in agriculture" by Arden Andersen is a great source.
"So your upside down tree" is due to the loss of the auxin dominant shoot. Atleast from what I know.
The top is now setback and it will take time before a new shoot comes out and starts being a sink again. So it might look like the lower part grows faster in contrast to the now stunted top shoot.
I only have Penang 88 seedlings and they grow like the others, i think the shape of the tree have more to do with soil, sun, shade. These are all zibethinus after all but even the graveolens, kutjensis, oxleyanus and hybrids have same or similar growth pattern to zibethinus, from my field observations i have deducted that the environment dictate the shape of durio more then the variety etc. However the vigour is different, graveolens is really vigorous compared to the others!
Potential root stock for anyone grafting durian.
Root's are in one way similar to shoots.