This is an old thread, but just wanted to post to say thanks to the original poster and the people who replied.
I had a similar problem to the OP, and when I tried the paper calibration method the bad area just moved to a different corner. 😀
I printed the grid from the OP post, and then (as one of the replies suggested) just manually adjusted the screws until I got a good print.
That worked a treat, and my UM2 is producing the most uniform prints I have ever seen.
Thanks
Darren.