From the initial testing, it seems like the amount of tp you gain from casting is based on the MP cost instead of the tier of the spell.
For example, I got 9 tp return from water III which cost 98 mp to cast. Got 3 tp from Drain II which cost 36 mp to cast. Got 8 tp from Thunder II which cost 86 mp to cast. Got 4 tp from stone II which cost 43 mp to cast. Got 3 tp from bio II as well.
You guys can test it more but that's the initial finding. I am not sure if store tp effects it anymore as I am /sam and the tp gain stays consistent with the MP cost/10.
Interesting nonetheless.
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