Less than half a season is a small sample size, especially when you're dividing it by home and away. I wouldn't worry about the park.
Also, you seem to be underusing Mathewson. He's your best starter -- you should be sending him to the mound whenever he's not tired.
Finally, you drafted too many innings for an OL. If you're the sort of person who pays fairly close attention to your team, you can easily get by with 1200-1300 drafted innings (provided you use your AAA, draft good pitchers, and don't use Coors). You pay for two things when you draft a player: quantity (IP or PA) and quality. Cut back on the former and you can afford more of the latter.