It's not explicitly stated in the Toss entry in the REG but there are a few things we can key in on to find the answer.
A toss ability allows a player to play an enhancement in a different way than usual;
Enhancements discarded to the toss ability are played from hand.
Both of those entries indicate to me that the Enhancement is played, then a toss ability causes the Enhancement to have a different effect than it normally would have.
But what does it mean to "play" an Enhancement?
You play an enhancement by attempting to activate its special ability (or numbers in battle)
The conclusion I draw from all of this is that toss doesn't target the hand at all, but instead targets the eligible Enhancements that are being played in battle.