Extracting the substrate model using Calibre PEX

Hi all,

I am using a flow which includes Calibre PEX,
and I would like to extract the substrate model using the tool.
For instance, I want to know the parasitic resistance of the substrate
between the one P+ guarding and another P+ guardring 10um away, which
are connected to ground net.
Can't I extract them only (without any other active circuit) ?
I want to figure out the dependency of the parasitic resistance on the
distance among the P+ guardrings.

Any ideas or suggestions welcome.

Thanks in advance.

Angel Park