How do I need to cut the taproot?
Yes, what happens is that you are actually pruning the root. So what happens on top of the plant above the soil – when you prune it you get re-sprouting of the dormant buds – does also happen below the soil: the pruned root re-sprouts, and these re-sprouts do not have the problem of the “stored memory that tells him to grow rounded”. Instead of that, it sprouts and grows again as it does originally = vertically downwards. The new re-sprouts do not have the breaking power that the original primary root has, but they are far better than a superficial rounded growing tap root, that stays in the top soil where there’s none or just a little bit of water available for the plant. This is also the reason why so many trees fall down in cities with strong winds. They are just not anchored.