Manually Logged / Completed calls not showing on User Calendar in Zoho CRM

Manually Logged / Completed calls not showing on User Calendar in Zoho CRM

At present, when viewing our team calendar, completed or manually logged calls (created in the contact record) aren't visible.

I've tried creating test calls both from the Calendar and from the Contact record, and so I'm not sure where the issue is -
1. if they're not being assigned to that calendar at all, or
2. if they are being assigned but completed calls are hidden from view

While we do have scheduled calls booked in on occasion, our business takes ten times that number in unscheduled incoming calls and we're not always aware in advance when a spike in demand could happen. It would be useful for us to be able to see these at a glance in this calendar view. 

I know some reports would be able to show this, however these are less... immediate or quick to check if that makes sense? Having these displayed visually on a calendar would allow us to assess capacity more mindfully 'in the moment'. so we can utilise our resource better, respond to peaks of demand but without compromising on staff recap & admin time.

Has anyone else experienced similar / know how to show what I'm looking for?