In order to weight yourself for free-diving correctly you have to perform regular tests, which are mandatory for your own safety. If you have different types of free-dive wetsuits calculate and test the amount of weights for each of them and always check your buoyancy at the beginning of your training/free-diving session.
Do not expect that your weight setup, which worked one time, will be good forever. Your body conditions are constantly changing; take your time to find the right setup. Use small weights rather than big ones. Small weights put less stress on your body, precisely on your lower back, and you can distribute them better around the belt, whilst making fine adjustments.
The design of Lobster belt allows you not to worry about the possible water resistance. Hydrodynamic properties of the sinker, due to it’s shape and material, negate the disturbance of water flow, allowing you to concentrate on diving.