Carisoti is of the same opinion as I_ Light and training are large factors (besides genetics,etc.). When growing photoperiod plants I train them using pruning, FIM and LST. to keep the colas as close in height as possible. For auto's I use LST only but have to really stay on top of that making adjustments as needed_ last grow two of them got away from me while I was gone for 4 days only. With these methods I get an average of 6-12 main colas with less than 4" height difference.
One thing I've found that seems to work well in a limited space where you may not have the room to train too far to one side or the other is to get some of those circular wire screens that can be found at almost any gardening store. They fit down into the pots on wire posts and the height can be adjusted as needed. The screen makes it easy to open up the plant as it grows, helping to keep the colas nearly the same height. They also provide points to anchor LST ties to. I got them initially because my grow space doesn't work well for SOG done in the traditional method. This works well cuz you can move the pots around without disturbing the LST screen. As the plants grow taller you can move the "screen " higher to keep better separation. The plants that I've grown with LST, FIM and pruning all seem to use more energy to produce more colas than height when compared to an untrained plant during the growth phase and during the flowering phase this is even more pronounced. Having more colas nearly the same height also keeps the maturity of the flowers more consistent and maybe even helps them to mature faster..but could just be wishful thinking?.