Hmm, not sure you understand how the XP bonus works.

The higher you get the quality percentage up the higher the XP bonus, it has nothing to do with the end results of the craft.

For example.

Craft 1 - You get an 18% chance at HQ'ing a Mythril Ingot and succeed.

Craft 2 - You get an 86% chance at HQ'ing a Mythril Ingot but you end up with normal quality.

Though the quality of the item is actual better in the first craft you'll still get less xp than you would for the second craft.