Ball Park Factors take into all account Runs Scored, the fact that 9 times a year or 27 times over a 3 year span or 11% of the games played or 5.5% innings are accounted for are from the Seattle Mariners.
Frankly I like the way espn calculates ball park factors -
2012 MLB Park Factors - Runs - Major League Baseball - ESPN ... It's less complicated but gets to gist of it easier and the rankings fall inline with Baseball reference.
Look at Yankee Stadium Year to Year in Ballpark factors the Variance is all over fukking place
2009 - 97
2010 - 113
2011 - 108
2012 - 100 ( And this year they set a Franchise Record for Most HR's hit)
OPS+ 100*[OBP/lg OBP + SLG/lg SLG - 1] Adjusted to the players ballpark(s)
You Take the Baseformula w/o the Pall Park Factor
Trout's is 162 (Actual 170)
Miggy's is 170 (Actual 165)
Take 100 as the Basescore: Angels Stadium is 92 (+8), Comerica is 104 (-4)
Thats how they get to 170 and 165.
I figured these Stat boys would take into account the road games as well but they don't or it doesn't hold much weight