User blog comment:Ixarising/Favourite couple./@comment-101.113.19.26-20140823162519/@comment-117.97.202.11-20140826173939

If I can recall the author has lampshaded that he only wants the heroines (AKA the harem members) to be the ones on the covers. If you will notice Gasper is on the cover for volume 16 and Kiba is on the alternate cover for volume 1

PS. If any of you say something about the first two volumes I already know. He mentions the heroines on the covers in one of the later volumes as the format that he wanted for his series. (Volume 13 itself I believe.)

Interpret as you wish. Everyone is entitled to their own opinion. But it all falls short as Ishibumi-sensei is the person who will decide what is what in the end.