Marketplace talk:Post Trade Requests/@comment-24.23.248.127-20120624185824/@comment-5182322-20120624204402

F and F+ cards do not give constant levels.

http://www.gree-support.net/entries/21603506-fusion-guide-6-24-in-progress-the-truth-about-f-f-revealed-pre-calculated-tables

You can see from my guide they lose experience gain based on level of base card and rarity.