I also noticed that "mount_effect elephant -4, camel -4" was the reason for horses fearing the more exotic animals. What would happen if we were to create a new mount category for units that weren’t mounted? For example, goblins are supposed to fear High Elves. Can we create a mount category called Elves, give it to all elves, and then give all goblin units "mount_effect Elves -4"? Is it just a form of classification, or will it have detrimental effects on Elven infantry units?
The mount categorys are hardcoded but even if they werent it probably wouldnt work. Horses fearing camels and elephants is caused by the frighten_mounted flag these both have.

Here also is the list of attributes for future reference:
That list dates from rome, theres new attributes been added and some of these dont work.

Also, arent feudal knights equipped with mail while brettonian knights have plate? Using them as a anchor might not be the best, I'd use a few units which have equivelants in the two systems.