The beauty of BBL is that allows you to fill the buttock area exactly where you wish to.
Just as an example, the butt implants can only be placed within the muscle layer and can not reach as lateral as the hips.
The fat instead can be injected anywhere to contour your buttocks exactly as you wish to. The main limit is the volume of fat you have available and - depending on the result you aim for - you might have to consider two stages surgery.
I usually show my patients pleanty of before&after pictures and this helps very much in understanding what kind of results we need to go for.
I would recommend to find a UK or European board certified plastic surgeon with clear interest and experience in buttock of surgery.
I hope you found this answer useful and I wish you the best of luck with your BBL.