In Curtis Granderson's last full season as a Yankee, he hit 43 home runs, 26 of which came at Yankee Stadium. It is easy to assume that many of those were with the benefit of the short porch in right field. Thanks to the site Katron.org, we can use a tool to track the location of balls in play in one stadium versus another.
If we assume that balls that touch the wall were not home runs, then eight of Granderson's 63 Yankee Stadium home runs would have stayed in the park had they been hit at Citi Field (all else equal). Of course, as much as the porch is short in right field at the Stadium, left field in the gap is cavernous. Granderson hit three balls in play that weren't home runs at Yankee Stadium that would have been at Citi, all to left field.
Overall, the net difference in Granderson's home park home runs overlaying Citi Field's dimensions onto Yankee Stadium totaled only five of the 63.
2013 (shortened due to injury) - Net 0 home runs added at Yankee Stadium (of 2 total hit at home park)
2012 - Net 4 home runs added at Yankee Stadium (of 26 total hit at home park)
2011 - Net 1 home runs added at Yankee Stadium (of 21 total hit at home park)
2010 - Net 0 home runs added at Yankee Stadium (of 14 total hit at home park)