What rank is it? It also depends on your level and area. Example if your chocobo is below rank 10 and are in new area trying to raise it you may see lower xp. Just like when your doing a fate and your level is below recommended you get penalize. If your in an equivalent level and area xp can range. I use attack food gets an extra boost of xp, FC action can boost it as well, and make sure it's not capped. ( Have Tav. onions ready ) If it's just you and choco you should be fine, if multiple in party it can affect it.