Yes, phal season. What a great time of year!!!
I can't say I know the answers to your questions. In my experience, though, I've got one plant branching out now that didn't branch before. I've also got some plants with double spikes right now that grew single spikes last time, and one single spike that was a double spike last time. Other than a hybrid's genetic tendancy to branch, I don't think there's a particular reason why they grow they way they do. I think they just do what they want; if conditions are just so, and the stars are aligned just right, they double spike and branch.