You can enable or disable the in-call control button which is displayed during each call (it is enabled by default). This can be done for incoming and outgoing calls separately. In addition, you can check "Show button to add star" to mark an ongoing recording as important even before the call ends (a star will then be added to it automatically).

By default, long pressing the in-call control button enables its dragging to some other place. An alternative option selectable in "Long press action" is to hang up the call and then call back automatically. To make the in-call control button accessible before an incoming call is answered, check “Show button while ringing”.

Recording may also be started and stopped from the notification pane. If you expand it by swiping down during a call, an extra push button will be shown for this purpose.