My experience: bright light is necessary to keep internodes short. It also helps keep petioles short and leaf size smaller. Mine continue to grow inside in winter, but I usually have to cut all that growth in the spring as the leaves are larger, on longer petioles and further apart. Cutting these back to last summer's growth often results in a single new back bud.
My conjecture...which I may test this year: back budding is somewhat dependent on where light reaches. If the foliage is tight and shades the branch, it will tend to bud just enough to continue the branch growing. I've noticed mine has spontaneously backbudded further back on younger branches where I've opened them up to direct sun without having the growth tip removed. I'm talking still green branches or bark that is only 1-2 years old.
I've been struggling with how much I believe that conjecture with mine. My design is such that if I fully defoliate and it doesn't eventually back bud to fill in, I'll end up losing what I've been aiming for and will have to start again