How do I set the default country in the sign-up list to the same as the country in the company settings screen?

Change the first line in ~cpanel/shiva/psoft_config/hsphere.properties to:

STATE_COUNTRY = IE US CA

The first group of 2 letters is the ISO code of the default country (in this case it’s Ireland), the 2 other groups are codes of countries with states – they are required to build drop-down lists.
Restart control panel to activate these changes.