I asked them about that and they're very precise about it, it must be overall 3-5 eps with a minimum of 30 panels each.
Which means that if you post just a cover on your "first" episode, you'll be immediately disquilified since it doesn't meet the 30 panels requirement. Same for a short epilogue or thank you note.
I guess it's because 30 panels is the minimum to keep readers entertained and having extra episodes for covers or thank you notes would be cheating in terms of reader engagement since it would give you more views and comments for very little work.