I think there has been discussions on the legitimacy of those "arrangements" in the past. As a basic rule, Dragonfruit seem to grow on downward growing "arms". I remember reading somewhere that they use that type of display to market the plants. In the picture the fruit possibly outweights the cacti. Although you could cut your dragon fruit back to two feet, you may not have fruit until it grows back. Dragonfruit usually has to grow to a weight of about ten pounds (the cactus) before it will fruit.

ok,thanks.