What Is the advantage of using thick metallic strips to join wires In a potentiometer?

AB is a potentiometer wire (Figure). If the value of $R$ is increased, In which direction will the balance point $\mathrm{J}$ shift?

While doing an experiment with potentiometer (Figure) It was found that the deflection Is one sided

(a) the deflection decreased while moving from one end A of the wire to the end B.

(b) the deflection Increased, while the Jockey was moved towards the end B.

(i)  Which terminal $+\mathrm{or} -\mathrm{ve}$ of the cell $E_1$ is connected at $X$ in case (a) and how is $E_1$ related to $E$ 

(ii) Which terminal of the cell $E_1$ is connected at $X$ in case (b)?