Ratings in match preview

I noticed this strange thing in match preview which I don't understand.

This is my lineup - 3-1-2-3-1.

Attachment 140674

And these are ratings in match preview.

Attachment 140675

Player in DMC also hase a DC role, so I try to move him back and change formation to 4-2-3-1. And this happens with ratings:

Attachment 140676

Same player moved from DMC to DC, defence rating stays the same and midfield rating is 7% higher? How come?

And similar situation. Same initial lineup, now the player in DMC position is a bit weaker.

Attachment 140677

This DMC also has a MC role, so I try to move him to midfield and change formation to 3-3-3-1. Now ratings look like this:

Attachment 140678

Same player moved from DMC to MC, midfield rating stays the same and defence rating is 11% higher... Does anybody understand this? :confused: Should I follow there ratings or are they useless?