Is there a way to have only one or two of the 3 coordinates be taken into account for completing a quest? I didn't find anything on wiki, nor in other sources.

You can sort of do this using quest logic.

Instead of creating one quest with a location task create three using the OR logic operator so that completing any of those quests unlocks the one that provides the Reward, while also using NOR logic so that you also immediately lock out all the other options.

You could make that final quest have no tasks, or let the players decide when to turn it in by completing a simple checkbox task.

You can name and describe the three quests as different options . . . and if you want to get fancy you can even have them unlock and show a "result" with different rewards depending on where your player chose to go; though that moves outside the strict boundaries of what you wanted to do.

Hope this helps :)

               Quest 1  -NOR logic link - Quest 2
              |                                  |
    quest 3 with OR logic requiring one of the two in order to activate