Looks about right. Possibly a bit lower-down, (1/16" or so) otherwise you end-up with only two cola's, and a bunch of weirded-out half-leaves. It's a technique that's hit-or-miss, at least with me. Sometimes I get two cola's, sometimes up to 6 or 8. If doing this to more than one plant, beware of the likely uneven growth.
Now-a-days, I just 'pop' the top, and am happy about the two cola's. You can also 'pop' the tops off the two resulting branches, making four cola's, but after that, it switches to alternating internodes. (depending on when you started topping)

If doing one, might as well do 'em all. Normally I'd say to experiment with only one...but with this technique it's kinda hard to screw-up. (FIM stands for "fudge, I missed" anyway)
Can try a bit higher than your line and a bit lower...and see which you like better...and spend the rest of your life trying to duplicate the sucessful ones, lol. They'll all survive, but single-shot multi-branching is hit-n-miss. Depends on what the repair tissue decides to become, from what I understand.