7 – How to allow access to page variant (Page Manager) if user belongs to list

The Situation

I have an ECK entity called “Event” in my Drupal 7 site.
I have an entity reference field on Event that collects users who flag the Event with a non-global flag called “Sign up” via a rule.
I use Page Manager to control how an Event entity is shown to the users.

My context:
Edit relationship “User from Event (on Event: List of attendees (field_attendees)”
Event: Entity being viewed
Identifier: User from Event Attendees (field_attendees))
Keyword: event_attendees
Delta: 0

Here is the Selection Rule:
User: compare logged_in_user is User from Event Attendees (field_attendees)

The Problem

As you can see, one of my Page Variants has a selection rule that checks if the logged_in_user is on the list of attendees but it doesn’t work because the selection rule takes a “delta” and that means that it takes a hard coded integer to select one of the list. And if I leave this empty, it automatically takes “0” i.e. the first one in the list. There seems to be no option to set the delta to include all or any.

The Question

How can I create this selection rule to check if this user is ‘on the list’?