I think he's roaming a fair bit at Chelsea too, from what I've seen anyway. You have now doubt watched him more though so I take your word for it.
Yeah he is, but I said this to Pete which explains a difference.
"As for having a free role, that's true to an extent, but he's still always predominantly on the left, so it isn't comparable to Silva who drifts all over the pitch, swapping postions with other players.
Plus, when Mata comes inside, no one swaps with him to go out to the left wing, which if you watch Chelsea causes problems as they become very narrow and predictable. A lot of the time the only pass he will have on is to the right wing, as no ones on the left flank. Contrast that with Silva at City who when he has the ball in the middle will have passing options all over the pitch, Balotelli has a tendency to drift wide left, against Arsenal for example he did this alot, Aguero and Nasri likewise drift to the flanks, stretching the pitch. This gives Silva numerous passing options and creates space, Mata on the other hand often drifts in field, but as no one is on the left the defensive line just moves with him and he really has no where to go. Watch Chelsea play and look out for it, it always happens."
He does roam, but it causes issues. For example the Arsenal game at the Bridge he actually had an average position which was more central than some of the midfielders. So that implies he was roaming an extreme amount. But like I say, it doesnt benefit him or Chelsea, as no one rotates with him, so no one stretches the pitch.
Another comparison with City is that they have without a doubt the most attacking fullbacks in the league, it used to be Chelsea, but now it's definately City, Richards especially gets forward more than any other fullback I can think off. This again stretches the pitch and gives the central playmaker Silva, more options. When City play their best football all the players are rotating, there's space which players run into and the pitch is at its widest. This gives Silva such extensive options, sometimes he'll have a pass on to the advanced over lapping fullbacks, a through ball to the forward, Dzeko or Balotelli, or maybe Aguero or Nasri who drift around him. That's actually why I think Ballotelli is now preffered to Dzeko, he offers more fluidity as hes more comfortable moving around the pitch.
In contrast, Chelsea are completely stale. They always have been to an extent, but it's ridiculous this season. Drogba's a target man who offers little movement up front, but the worst aspect is undoubtedly the midfield, it offers zero going forward. A midfield three of Ramires, Meireles and Mikel is extremely defensive. AVB seems to have clocked it's too much and dropped Mikel, but Romeu, whilst a better and more technical player, has been given the same role, so it hasnt changed anything attacking wise.
In the past they could get by with this defensive/solid midfield approach due to Lampard being a threat from the middle and getting 20 goals a season. But now that he doesnt have the energy to get forward the midfield offers no threat. In practice what that means is that when Mata drifts in field, he has no one to pass to. There's little in the way of runs from midfield and Drogba doesnt have great movement. Added into that, he can only really look to one flank, the right one, as theres no one on the left. It means they are completely stale in attack and cant open teams up.
What I'd do is move Mata to the middle and drop a midfield player, Mikel in my opinion. Then play a new left winger. This would open the pitch up and give Mata room to operate, plus it would provide another attacking threat.