AR Three object touch detection

Hi There

I am trying to create a game with Three and AR. You can access my process here:
http://group.skillsofthefuture.co.uk.
Here is the marker image I am using which is best when layed out flat on a desk:

There is a rocket in the centre and then there are rocks/asteroids falling around it. The objective is to tap the asteroids and destroy them, there will be a score but I can handle that later.

At the minute I’m struggling to get the rock that is being tapped. I assume this is got something to do with camera distance to the marker is not being taken into account but I can’t figure out how to resolve it yet. Any help will be very much appreciated.