I'm going to test it myself when i have time and update post.
It's a theorical amount of XP.
So, it won't work.
so (for Osamodas)
- use dodge and/or HP food
- pick 1~3 Xel Present mobs
- pray for big map layout
- kill most of monsters with help of summon until there will be only one
- run around map like idiot and block enemy with summon
- spam gurgling/magpie/other spell you need to level up on empty cell
- do it for 60 turns (prepare some cool music or watch movie while doing this)
- kill last monster end fight
- get tons of spell exp
As I said, it has not changed.
If you use only one spell in a fight, he gets 100% of spell XP available, no matter you used it one time or a thousand times.
If you use 5 * 4 AP spell, and 3 * 3 AP spell, the 3 AP spell gets (3 * 3) / (5 * 4 + 3 * 3) = 31% of the spell XP available and the other has (5 * 4) / (5 * 4 + 3 * 3) = 69% of the spell XP available.
That's what I meant by how many times + AP/MP/WP cost.
Note that spell that can't gain spell XP doesn't count into account.
So if you use 10 * 4 AP maxed spell and 1 * 2 AP spell, the 2 AP gets 100% of the spell XP available.