If you insist on topping, I would remove as little material as possible, just pinch out the growth tips on the end of the branch.
Training (for me) is more about preventing unwanted growth and encouraging growth where I want it. Some people treat it as a simple method to take off all the unwanted growth after the fact.
The problem is plants grow in 4 dimensions, time being the 4th. Any growth will affect the other parts of the plant, so I don't allow the plant to waste energy or space on unwanted shoots and branches.