Last season he got two goals and an assist away from home against Newcastle, and his record home and away was identical - 3 goals, 2 assists. This season he's been significantly more productive at home, we can all see that. That said if you take a look at the two half-seasons together the most obvious underlying trend is that Mata plays well when we play well. Mata hasn't been as productive away from home this year because we haven't played as well away from home this year.
We've played 9 away games; lost 3, drawn 4 and won 2 including the losses against MK Dons and City, neither of which Mata played in. So I'd say his away form is reflective of our away form this season and the reason he was equally productive home or away last season is because we were equally inconsistent home or away last season.
Some players are more comfortable, confident and composed playing at home and that may well be the case with Mata, but teams being more physical? Come on. That's the kind of rubbish Paul Merson comes out with.