Q:

Contact pressure vs contact area

I'm learning to weld. I've realised my earth clamp is limited. The spring is weak and its contact area is small as it's tooth shaped.
Researching better clamps, I see clamps which have threaded bolts to clamp the jaws against the workpiece tightly. It is my understanding that unless you are clamping something malleable such as lead, increased clamping force wouldn't increase the contact area, unless such force is applied to leave indentations in the workpiece.
So I've been looking for clamps which have larger contact areas, and magnetic clamps seem to have large flat brass areas rather than pointed teeth which will be pressed against the workpiece with moderate spring pressure.
How does increasing clamp force increase conductivity, and is contact pressure really interchangeable with contact area size?
To be clear, I'm aware different clamp designs are more suited to different applications, but I'm specifically asking about the properties of electrical conductivity of a larger area being pressed lightly, vs a toothed (i.e, small) area being pressed very firmly.
Toothed clamp design:

Magnetic design with brass flat contactor:

A:

There is a proportionality between the pressure applied and the contact conductivity due the microscopic roughness of the contact surface that make the real contact surface much smaller. Applying a pressure flattens the surface increasing the contact area.

In some amount increasing the macroscopic area while keeping the same force doesn't increase the conductivity because the per square inch force will decrease proportionally. 
See here a much detailed explanation. 

