Tactics or team gelling/formation understanding?

Poor play and results - How do you know whether or not your tactics or whether its the fact the team is not used to playing the new formation?

Morale within my Newcastle team is very good, we've scraped a few wins early in the season (after completely falling apart in the final 10 or so games tail end of last season dropping from 2nd to 5th...) and I've bought a handful of new players. Some of them perform, some do not. Some of the signings I made in Jan during my first season are still awful (Carrick 18m, Moutinho 14m) and very little seems to work.

Two thirds of the first season and we were doing very well, everything seemed settled. I brought some new players in and it didnt seem to upset the team too much, we continued to win. Beating the likes of Arsenal 4-0 at home, beating Man U, Liverpool etc. Struggled at times against the weaker teams and we rarely scored that many goals in a match but we had the best defensive record.

I would often shout (virtually through instructions you understand) at the players for performing badly and some players became upset. The whole team quickly became absolutely rubbish. Beyond poor. Nobody could put away chances when they were simple tap-ins. Its as if a switch went off and the team became hopeless. I struggled and we fell away in the title race losing many games. I experienced what Keegan must have

The new season arrived and I've brought new faces in, not many that play in the first team (perhaps 4) and I cannot settle on a tactic. Last seasons seems not to work and I'd bought for that formation (4-1-3-2). This season we've started out fairly well, although I'm still dismayed at how hopeless players can be at times.

Is this down to the fact I need to leave my formation to bed-in so to speak, despite results, before I can see whether the players are able to adapt? I wish the Ass Man would tell me something about changing formations and the effect its having on the team. I cannot tell whether my formation(s) are rubbish or the players cannot adapt. At present I'm guessing the game is telling me I shouldnt keep changing formations in search of something with promise because players miss simple chances. If this is the way the game behaves, its really quite disenchanting, world class players cannot pass, cannot shoot properly... it can be quite frustrating! I can understand results being poor for a while, but it appears to reflect really poorly on individual player skill.

So... how long to you leave a formation to set in before you decide whether or not its going to work?

Any formation should be successful, it depends how you implement and whether you have enough quality players to implement it. I would never change formations as amanger of a club mid season if I thought my tactics were not working. I change tactics but not formations. The only time anyone may change formations mid season is if you have an injury crisis and say you normally play a 4-2-4 but you only have 1 fit forward player or if you are playing a really strong team then you may also switch but I never switch.