I was just about to post the same issue, my coolant light came on about a month ago was about the same level as your picture so topped it up. About 2 weeks later below the min line. Topped it up 2 weeks ago and its half way between max and min line. I think i have a leak.
Just great im out of warranty, just had the air intake pipe oil leak problem fixed which cost me as warranty has run out, my GTI has only done 33,000 miles. Rapidly loosing faith in the MK6 engine.