If you want the horizontal spreading growth-form of Hyg. pinn. the trick is to constantly trim away the dominant branch(es). Those are the bigger,fatter and up-right growing ones. By removing those, the plant will be much more willing to grow more of the horizontal branches.
New dominant branch(es) will be produced again and again - and must ofcourse be trimmed away again and again.
- and yes; you can start trimming these dominant branches right after in-planting, or even before you actually plant it. If requirements of this plant is met, it is really a surprisingly virile plant, capable of producing numerous branches in short time.