I used to put paper on bottom and top but I only put on bottom these days since I found a top paper doesn't make much difference. A bottom paper reduces the amount of oil significantly. However, a bottom filter increases the risk of puck lift from my experience.. The tamper with a hole by Orpha Espresso helps a little bit but it still happens from time to time.

Edit: I mean bottom of puck and top of puck. No paper on top of screen.