Calls to IVR, External and Queue get added to alert-info field in the INVITE and match whatever is set in the template.
My Yealink's "default" ringtone is "Common" which isnt specified by 3CX.
Therefore, I have to modify a template to adjust common to Ring2.wav or I log in to the GUI > Account > Basic and change ring type to Ring2.wav so internal calls that dont match the above alert-info.
Create a Call Queue then route all external call to that call queue and assign a Single Ring (Ring 1) to that call queue and set it up for each extension's.