I don't think this is correct. After reading all of the posts from the illegal formation thread it appears that "You need three midfielders (yellow dots), and at least one of them has to be a (DML, DMC, DMR, ML, MC or MR)".
The formation in question 5-2-3 has been played many times by the members and from what I have seen it has received 20% possession each time.
Player out of position should not result in 20% possession unless it's a GK.