Training with higher level fighters
I have a level 30 U Citrine but am leveling Master Jade (currently lvl 30 U+), so I dont necessarily need 2 earth fighters. How big is the bonus gain on an already leveled fighter when you train a lower level fighter with it? Is it worth feeding my Citrine to my soon to be level 1 U++ Master Jade or is it just too much XP-loss? Better to save it for future possible Citrine leveling?
Also another question which is sort of the same: if I have many of the same uncommon - is it worth training them with eachother before training another fighter (not the same as the uncommons) to get the xp-bonus from "same fighter" or do you lose exp when feeding a higher level fighter to my main fighter?