There is a pretty strong takeaway from this game that adds on the top of the other empirical observations of the last 2 months:
-> 3-5-2/3-4-3 works against good and top sides. Evidence so far says Yes when we faced PSG, Sevilla (2x), Sociedad. That's it.
Vs Osasuna it did the job, but we didn't create enough in that game.
-> But it does NOT against the common fodder of LaLiga and Europe. Wasting the 1st half tonight against a well-drilled double-decker bus says a lot.
It happened again vs Huesca at home. We struggled a lot in that first half too, and Koeman shifted to 4-3-3 at some point in the 2nd half which worked.
Another instance, the game vs Eibar at home in December when Koeman experimented with 3-5-2 in the 1st half, we created 0 and got threatened on the counter.
Then he reverted to 4-3-3, we created some, but there wan't enough time left.
I haven't yet come to any conclusive account on why this happens, it probably has to do with how the fullbacks/wingbacks commit when going forward and change numerical superiority. There is a tight balance there.
Based on the observations above, I think Koeman should go with '3 at the back' in the following games: RM, Villareal, Valencia, Atletico, with Levante being a question mark
All the rest should be 4-3-3/4-2-3-1