Contacts on Chart

I'd be grateful if someone could let me know what it is that determines whether a reported contact appears on the chart as a square mark. Sometimes they show sometimes they don't. I'm in Sept 1939 playing 1.4b/TGW on 97% difficulty (-3% for Event Camera availability). Is it something to do with the quality of the crew? It also seems that this is linked to the ID'ing of the contact type when looking through the attack scope. Am I right in thinking that if the contact is ID'ed by the scope (Eg. 'cargo' shows on the Notepad) then the square mark shows on the chart??

Thanks

KC