Could quite possibly be a factor.
Depends on a lot of things.
I think strain is prob the biggest.
I've got a bunch in same size pots, but branching differs a lot.
But usually, smaller pot = less branching.
Strains are from DP, which are known for heavy branching. That's why I am surprised that only one of them is okay in that aspect.
Also, around them is not much shadow, only little grass which is way below them.