Important: There are two ways to assemble the H-carriage, take a look at this picture:
(while it's for Anet A8 this picture just shows the idea).
Moving the central plate beneath cuts 6 mm of height. That's why this thing has two designs: 17 mm and 11 mm of height. Choose the one you need !
As you see from the picture it moves the top part of the belt lower to make it parallel with the bottom part.
Also, you'll need the longer screws.
After this tiny upgrade the carriage goes much easier.
P.S. photos shows 16mm block height, not 17mm, because of this it may look like belt lines are not parallel.