For crying out loud, use some critical thinking skills. That is, if you're even capable of it.
Your beloved FRAA stat makes "adjustments made based on plays made, the expected numbers of plays per position", etc.
As has been pointed out, the 1985 Yankees had an extreme fly ball pitching staff in relation to the rest of the league.
This means that Henderson, in CF, would have more fly balls hit to him than would an average CF, thus artificially inflating his opportunities in the field. This would artifically distort and inflate his FRAA.
Likewise, Mattingly at 1B would be handling fewer ground balls than league average for 1B would expect, thus artifically deflating his opportunities in the field. As with Henderson, this would artifically distort and deflate his FRAA.
Get your head out of your *** and try to understand how to apply your beloved stats correctly.
YOU NEED TO PUT THEM IN CONTEXT!!!