Hello again and sorry for the late (very late) reply. I want to follow up with the results I got after following Geoff's advice and the response I got back from FlashForge support. So I've sent them a video of me doing a measuring of the print bed with a dial indicator which you can find here https://drive.google.com/open?id=0B8...zRZRjlZNnJFNnc , and they said:

We notice the dial indicator is not fixed well. It move a little when carriage move. Even if you measure a difference of 0.2mm, it may be caused by plate, because the rod guide and bearings straightness tolerance is +_0.1-0.2mm.
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> If you think it affact printing, we suggest you to print a first layer at 0.2-0.3mm, or add a raft as you already did.


Adding a raft for models with a small surface finger print would compensate for the tolerante thay are talking about, at least for me it did.