Thank you for feedback. I have spend some time thinking about the placement of returned pieces, but I have came to the conclusion that a a single pile will be 1, easier to implement and 2, player will know exactly where to click and will not be wondering around, since it can already be bit chaotic :) Also, if player is focused, it is quite easy to know which of the puzzles was removed last and it will be on the top of the pile.
As for the second point, I wanted to implement few more things in order to make the highest row more relevant, but I had to step away from that as I wouldn´t be able to finish the core stuff on time. So now you can only reveal the score and number of lifes.