Well, the usual rule of thumb for cartridges is making sure the weight is closer to the pivot what the end of the arm.
So, if the cart is heavy and the weight is nearly off the stub, you need to go heavier. If the cart is light, and the weight is right up to the pivot, go a bit lighter with the weight.
There is a theory that the closer your weight is to the pivot, the better sound you will get. That said, I only have one weight, it's near the rear of the arm and think it's just perfect lol