I have lots of carpets, both Haddoni and Gigantea.
I lost several fish to my carpets.
The times that the fish are most vulnerable are:
Spooked due to you are doing something to the tank
Newly added fish, chased by other fish
Certain type of fish, mandarin (1/2) and Orchid dottyback (lost 3/3) for me. I think I will need to add Potter Leopard Wrasse (lost 2/3)
You need to have a reasonably large tank so that the fish can easy avoid the anemone. Don't have anemone tentacles against the glass. This is essentially a trap for fish. The glass keep them from been able to avoid the anemone.
Don't put any fish that you absolutely cannot loose in a Carpet tank.
Magnifica is a much safer anemone for fish. I have never loose a fish to my Magnifica.
Blue Carpet anybody?