Sharing option (no one or share with the organisation) vs security levels for shareholder

[GO]

I am about to set up security levels to some of our request types and found the following issue.

I selected a security level with a certain space role (shareholders) to enable visibility for a certain request type. If I search for a concrete ticket / request (which was created after setting up the security level) with that request type in the portal with that certain space role (as a shareholder), the request / ticket is not visible. I assume it has something to do with the privacy setting of the ticket created?

By default, all the requests / tickets created in the customer portal are set to private. 

I assumed, that security levels always override portal sharing, even if they are shared with no one, by default.

Meaning, if a ticket is not shared, it is also not visible to anyone, only for the customer (reporter), even I set the security levels?

If it is true, how should I set this up correctly?

Would this be the solution? : Enable sharing with the organisation by default and set the correct security levels in each request type? 

[John Funk]

Hi GO,

The Security Levels will only reduce the work item visibility for work items you already have access to. So if the Work Item (ticket) is not in the Request Participants field (shared) then adding the Security Level will not give you access to the work item.