Based on 1 match (I'm sorry but it's the only 1 I had so far which was not important/biased by bonuses, etc...) I can say possession calculation is good, not accurate, but it gave me a good hint on how to play. There is a big problem though, and it's feedback from matches: the "live action" shown during matches was already a joke before the patch, now it's even more chaos because it's based on the system read by the game (and I don't think was updated at all).
For example: I play with a slight asymmetric 3-4-3, with DC/DMC in the middle who pushes forward, wide wingbacks attacking, and narrow winger as inside forward. The game reads it as a 2-2-3-2-1, so my AMR and AML are actually shown playing as AMCs, and if I set them as wide as possible, it doesn't change nothing as of match shown because the system read it's stil the same, and it's linked to some "recorded plays" (of a 3-4-2-1 I think). Possession as shown in statistics do changed a bit but I'm not sure why and I will test this more. As of now I'm thinking of try ex-illegal formations as opposed to standard ones, to evaluate the importance of "rectangular greenness". I crushed a team with same %, by playing possession based attacking football using single players in free from opponent's players cases, and tweaking my other players in crowded zones of the pitch to lighten up the "greenness" as much as possible,. The trick could be doing this, while maintaining a standard formation like 4-3-3 or 4-5-1.
That's it, good testing to you all.