Here are 2 possible solutions.
Solution 1:
You will need a matching attribute in PrimaryContact pointing back to NSCPers. For the purpose of this example, I will call it MyNSCPers.
Your rules could then be:
If PrimaryContact is NEW and PrimaryContact.Same = YES
Then PrimaryContact.Address = PrimaryContact.MyNSCPers.Address
Solution 2:
No matching attribute is needed, but this may not meet your requirements exactly.
Have a process that creates the PrimaryContact and allways sets the PrimaryContact.Same attribute to 'Yes" and the PrimaryContact.Address to NSCPers.Address. If the addresses need to be different, the user will need to manually change them.
Here are the details
Create a process with the following actions:
ENTER NEW PrimaryContact WITH PrimaryContact.Same='YES', PrimaryContact.Address=NSCPers.Address
In your NSCPers form, for the PrimaryContact attribute where you check Generate "Add New" button', go into Settings... select custom implementation and select the above process.