Constituent Search - post code in all addresses

Folks,

After many years of being sheltered by working in a consortium I'm now in the exciting world of system management so finding myself rusty in some areas.  Hence a couple of simple questions on the forums!

I find that when using the Post Code as a parameter in the Constituent Search Screen (both single line and basic), only the postcodes in the address marked as primary are searched.  Postcodes in addresses not marked as primary are not considered by the search.

I'm sure it's an easy thing to change but can't find anything here or in the Help System that points to how to do this.  T_DEFAULTS?

Martin