That is interesting. I am assuming that the game is looking for Specific sections to jump to. If you use This Spell in This Index then Jump 1C further to use the actual spell. I'm assuming that Asura and Bahamut are handled a little differently though. That may be worth a look.
... you mean because those are the only two where the order of the *cast* spell is not the same as the order of the *effect* spell, right? I've thought of that as well. I've also considered that maybe the different order has something to do with the multiple effect spells associated with Asura.
Don't know how much time you've spent looking at the game's graphics, but it's also worth noting that:
a) the summoned monsters' graphics are all grouped together,
b) they are the last monster graphics that appear (beginning at 68A18 - the earliest monster graphics begin at 48200),
c) they follow the same order of appearance as the effect spell,
and d) there is a large amount of non-graphical data separating the summoned monsters' graphics and all other monsters' graphics
Incidentally, I've also learned how to make an enemy look like a chocobo (change the graphic pointer to C217 and the "size" to 01), or a sylph (C5D4/C5E0/C5EC, 00). Not very useful knowledge about summoning, but a fun side effect of my search. The other non-enemy summons (Shiva, Indra, Jinn) are all irregular sizes, so while I'm sure it is possible, I don't know enough about how the irregular-sized monsters are encoded to make them enemies.
Some pieces of info I'm missing that surely are key:
- the location of the subroutine(s) for the effect spells
-also, I'm sure the effect spells must also have a separate range identified somewhere. If that could be found, then maybe changing the range of the cast spell wouldn't cause the party to permanently disappear (not to mention possibly make other monsters summonable).
(SORRY, this is totally off-topic)