When being in a party, the icon on the map for your party member should be ON TOP of the icons on the map. I should not think I am alone or not see the player at the event because their blue circle is behind the regular map icon.
When someone says im here but then we don't see them on the map it tends to get annoying after a while.
I've seen this too when playing with 2 others. Some ideas that can help are:
Grouping map icons together when they are too close.
Having them show as one icon that expands to show each icon to the top or bottom depending what is further away from viewport edge.
I feel either of these would greatly enhance the ability of putting map markers without them conflicting (z-index wise) with existing map's POI's.
It's true the visibility of the other members of the group must be greater, we have trouble finding each other, joining each other. It can make the game much more interactive with others. In addition to being able to share quests.