[SalesForce] profiles vs sharing rules

Let me guide you to a great SFDC document across contact sharing. https://help.salesforce.com/apex/HTViewHelpDoc?id=contacts_sharing.htm

Now whats important there is the 'considerations' section which says -

• If your organization-wide default for contacts is set to Controlled by Parent, the Contact Access options are not available when sharing related records like accounts; instead, all access to contacts is determined by the user's access to the contact's account.

• If your organization-wide default for contacts is Controlled by Parent and your organization-wide default for accounts is Private, you can’t view contacts for accounts you don’t own even if you have the View All permission on the account object. However, if you own a contact on an account, you can view other contacts on the same account since access to a parent account always gives you access to the associated child records.

I guess the second point is pretty much resolution to your query :)

Cheers,

Salesforce R&D has confirmed that this is intended functionality.

They agree the documentation here isn't very clear so they have updated the knowledge article to include:

Contacts may not be shared independently from Accounts, so Contact Sharing Rules are not applied (even if they are defined).

Help Article: https://help.salesforce.com/articleView?id=000004005&language=en_US&type=1

Success Idea: https://ideas.salesforce.com/s/idea/a0B8W00000Gde90UAB/contacts-without-accounts-ability-to-make-them-not-private