I misunderstood...I thought he meant putting a card on top of the conical to keep it from moving or something...but if the question was about ALSO putting a card over the powder in addition to the Oxyoke wonderwad, then no...not only would it serve no purpose, it would be counter-beneficial to have a card on the powder behind the Oxyoke wad on top.
The Oxyoke wonderwads are injected with lube which liquifies under heat & pressure and coats the walls of the bore as it's moving up so the combustion fouling that's developing behind it is kept minimized by that lube.
If the card was underneath the wad, it would prevent the lube from coming into play with the combustion and scrape any lube that made it to the bore walls right off of them.
Seeems like there's been an enormous amount of "armchair OP card theory" introduced to this forum during the past year...