Maybe we could go some way to minimise the rebound problem by careful orientation of the faceplate in respect of the line of fire. I'm thinking that the target could be placed so that the faceplate is inclined downwards or tilted towards the shooter by say ten degrees. Pellets hitting the paddle are very unlikely to come back through a small kill zone, and at short ranges the pellet should have enough momentum to overcome the additional work of tilting the plate back to vertical before the torsion spring makes it fall.
Perhaps also we might consider some kind of shroud?
Bounce back is something to be considered; we had a visitor's day for the public at our club soon after we opened in 2003, and a 25 calibre pellet came back from hitting a steel scaffold pole at ten yards. I put that down to the pole being "springy" and the pellet being slow and not shattering on impact. We don't use scaffold poles any more, oddly not many of us shoot 25 cal either.