Question

Why should the balance point be near the middle point of bridge wire?

Answer 1

At the balance point, half of the wire weight is on each side. If the wire has constant cross section, the balance point should be in the middle. The resistance of the wire is determined by the wire cross section. if the wire has an area of smaller cross section, that area will have higher resistance and get hotter (not good). So the best wire has constant diameter and a balance point in the middle.