Too far, has to be sent out on one of the platforms that you're allowed to send on based on the Arena Description.
----------
With the Gym Leader (challenger) starting at the Northern edge of the arena and the opponent (acceptor) at the southern, the layout of the gym is as such, with the trainers able to release pokémon on to the two platforms nearest them if desired:
----------
You can send your Pokemon somewhere on your half/side of the arena though, just not all the way to Kush's side. If his Pokemon was on your side of the arena I'd let you send a Pokemon right next to his.
