You can top them wherever you like but the most important part of getting a flat canopy is keeping the top two nodes flat while the lowers catch up. Then as each lower node reaches the top it gets held there until the nodes below it grow to that level, and so on.
That's how I do my plants:
If you top down a few nodes you can try your hand at cloning that bit, but you'll obviously end up with fewer branches in the end.
That thread is for photos or autos, but it's really for those just doing LST without topping. That's how I did
this without topping (that's a 4' wide table and a 10 gallon pot).