Height is not all you have to take into consideration. Those rules apply to a plant with a single main stem that has not been topped or trained.
Once you get into a plant with some side growth, you have more leaf mass to support with those roots, and you need more of them.
I think that the problem you are having is actually related to, or worsened by, your plant already being too big for its pot.
That's why I asked about how many stems you had on your plant.