Inter coach Roberto Mancini is working hard to find the best formation that suits his current personnel at the club, he has implemented six different modules during the five games in the last 22 days.
He first tried the 4-3-3 and a 4-5-1 in the derby with Palacio as and Kovacic switching places, then he switched to the famous 4-2-3-1 of Mourinho at the time of the Treble, then tried 4-3-1-2 with Kovacic as a trequartista.
The normal trial period would be in July, but due to his appointment in midseason he is trying to adjust it as quickly as possible waiting for the January transfer market.
Source: FCInternews.it

And with all the results, Mazzarri stick to the same one! Thank God he is gone!
defensive: 4 2 3 1
offensive: 4 1 3 2
4312 until new players come
keep 4312 with flexible switch to 4231 but we definitely need wingers
if we have good wingers, think it will be 4231 formation.
He usually implemented it during his days in man city