The proximity seems to be driven from the postcode. When looking at results from a proximity search, the postcode areas entered will all be the same for the various postcode areas entered.
For example, searching with proximity from RG12:
Rg40 is 0.9 miles
GU15 is 5.3 miles
GU19 is 4.5 miles
If no postcode is entered, the SP doesn't appear in the proximity search.
You can see the postcode if entered by selecting "view a map of the area where XXX lives".
If no postcode, it seems to use a town to show the location.
For example this SP shows Reading as the first location in her list but has Bracknell as her "searchable" location (see map of where she lives).
She doesn't show in proximity searches but does show when searching Bracknell
External Link/Members Only She's not on HL but illustrates the point.