*bump*

Not familiar with Wax Jambu, but in bonsai pruning, root pruning and soil particle size are utilized, to some degree to control growth. You want young trees to grow fast, so a larger soil particle size means better soil aeration and faster growth, older trees you want to grow slower are often put in smaller soil particle size. That being said, smaller soil size/less aeration provides less than adequate conditions for roots, so one must be aware of the signs of root rot.

Again, It depends on the plants soil moisture requirements.

Please try slow releasing fertilizers, if the growth is due to fertilizers.
And also think an other way around about the water drainage, if the water drain is good then the plant will get thrive bcoz the root system. Now your plants are thriving for a ground if you still want to restrict them in the pot them pack them tight and use slow releasing feed.