Training Chocobos n Stables

[Dustytome]

Hmmmm as long as your Stable is at Max and your rewarding it favorite food the XP shouldn't be going down. It should be increasing from my experience unless that has been changed. At least that has always been , then again I was the only one rewarding it being a one man FC. Maxed it to rank 20 around the time HW came out.

The xp scales up yes, but the % of the total you get past lvl 10 goes down. Just tested on a few chocobos in the stables (stable is sparklin clean):
lvl 7: 1%
lvl 12: .79%
lvl 17: .55%

Edit: Skimming posts and not thinking clearly... the issue is likely the stables needing to be cleaned as Zetsumei pointed out. It'll give the maximum experience reward if it's sparkly clean.