Why double contact structure reduces resistance?
Think of the plate as a sheet with uniform resistivity. 

Now consider that with a contact at each side, no current will flow across the centre line of the sheet. Why not? Because it will flow to the nearest terminal. So you could cut the double contact sheet down the centre line without affecting its operation, and arrange the two halves side by side.

Obviously you have halved the length of the sheet, halving its resistance.

But you now have two of them, connected in parallel....