This was the question asked by The Hardball Times when it comes to home victories.
Photi has the link at Fish Chunks and provides a good overview of the results of the article.
You need to click through to at least read Photi's synopsis or you could be all gung-ho and read the methodology and results by THT. (Which is never a bad idea.)
Now, I haven't tested what I'm about to say and it is just observational, but I don't think the overall results of the are article are indicative to the play of the Marlins at home.
The only large pro-Marlins crowds (over 20,000) the Fish experience during the course of the season are the home season opener and Camp Day. Since the 2005 fire sale, the Marlins haven't won a home season opener. Camp Day, which is a mid-week day game where about 20,000 kids fill the stadium and all of them rooting for the Marlins, is a little more sporadic when it comes to wins and loses. IIRC, and I'm not guaranteeing I do, the Fish lost Camp Day in 2006, won in 2007 but only after the campers left was the win secured and split the two Camp Days last season.
The Marlins do well in large home crowds that are mainly "hostile", i.e. when the crowd has more Mets or Phillies fans in JRS than Marlins fans. Kinda like playing on the road except the players get to go home to their families.
But when it comes to large pro-Marlins crowds, it seems to confuse them. They don't have any problem performing at their best in front of 1,000 very vocal and supportive fans at home. (I guess it reminds them of their high school days.) But put them in front of 20,000+ adoring fans they get lost.
I'm sure the players would love to have 20,000 or more adoring fans at every game and that they would adjust very quickly to the change and welcome it with an open heart. But as it stands right now, they do there best work when they aren't surprised by a bunch of people supporting them.
Kinda sad, really.
But whatcha going to do.