Motor starter capacitor components

Recently I determined that the failure of my powered garage door opener was as a result of a failed motor starter capacitor. This was easy to troubleshoot since smoke was coming out the bottom of the capacitor.

I was able to buy a replacement capacitor on eBay for $9.50 landed at my home. The garage door opener now works perfectly.

In an idle moment I disassembled the failed capacitor to see 'what made it tick'. As the pictures below show,  it is a regular waxed paper dielectric capacitor. I identified the failed area as an area where the paper was completely dry. Exactly why that section was dry remains an open question.

The capacitor is made up of 2 plates of dimensions 22 inches long by 2 inches wide and made of a thin conducting material with a rough surface. I understand that the roughness increases the surface area and thus the capacitance. We all understand how this works as a capacitor...

What is a mystery to me is the inclusion of a 3rd conductor made of the same material as the two plates. This piece is 48 inches long by 2 inches wide and appears to be overlapped by a few inches with one of the two plates. In other words in electrical contact with one of the plates.

Thus one plate has a  much larger surface area (I believe) than the other.

A Google search did not reveal the answer to me.

What purpose would that 3rd conductor fill?

Does anyone know the answer?

Outer protective sheath with specifications.

Removed inner components still rolled up

The two plates showing wire connecting points. The mystery 3rd element and the waxed paper dielectric.

Installed replacement starter capacitor bought on eBay