When you open a ticket on behalf of the customer - you can already specify the relevant contact - Please see the attached screenshot.

But sadly choosing a contact will only add him to the recipient of the ticket update - so he will get the tickets update along side the main contact of the client.

the same behavior is happening when you create a ticket on behalf of a client and when the contact opens a ticket by himself - the main contact always get all the spam...

This is something really problematic - you can see all the explanation here: