Facebook Banner Ad not mediation option for Tablet Leaderboard banner?



I would like mediate Facebook Banner ads to a Leaderboard sized ad on iPad. This isn’t working for me. Facebook Banner ads don’t show up as a mediation option. I can get Facebook Banner ads to be successfully mediated to the Mopub 320x50 Banner, but if I do that the MoPub Marketplace ads are tiny and do not fit the width of the iPad Screen. Is there a way to get the Facebook Banner ad onto the Mopub Leaderboard?