Transition to another layer is instant, you can't use lerp for it. What you need to do is change the sprite size before moving to another layer.
For example: run a Tween that will change sprite scale from 1 to 0.7 over 0.5 seconds, but keep the sprite on its original layer. At the end of the tween move the sprite to another layer using those long expressions to match its position, and restore the sprite scale to 1.