Thanks for posting!
I think the difficulty in hitting home run in Griffith stadium had to do with the height outfield wall.
From http://www.ballparksofbaseball.com/ballparks/griffith-stadium/ :
Griffith Stadium changed little throughout the rest of its life. Not only was it one of the smallest ballparks in baseball, but one of the hardest ballparks to hit a homerun at. Original dimensions were 407′-L, 421′-C and 320′-R with a 30 foot high fence stretching from the right field foul pole to center field that included the scoreboard. The fence in centerfield jutted into the playing field because the team was unable to purchase five houses and a large tree when the ballpark was constructed. Dimensions at Griffith Stadium were shortened slightly in 1956 when a 6 foot high fence was added in front of the left field fence shortening the distance to 388 feet.
Griffith Field:
As Forbes Field's dimensions, here is an excerpt from
http://www.ballparksofbaseball.com/ballparks/forbes-field/:
One level of seating extended to both the left and right field foul poles and bleachers were located in left and center fields. The scoreboard was part of the outfield wall in left field. Original dimensions at Forbes Field were 360 ft. (left), 462 ft. (center), and 376 ft. (right). . . .
After the Pirates acquired slugger Hank Greenberg they moved the left field in 30 feet to 330 feet after World War II. This area became known as Greenberg Gardens and later Kiners Korner when Ralph Kiner became part of the Pirates. Forbes Field featured an ivy covered brick wall in left and left-center field.
Forbes Field: