Does anyone know the mechanics for which Grit item you obtain after releasing a Pokemon?

Question

In PLA, is there a way to determine before releasing a Pokemon which Grit item it will give, based on level, effort level, alpha status, etc?

Comments

It's based on effort level but I'm not sure the specifics

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From experience, I didn't get a bunch of Grit Rocks until I started releasing alphas. But again, I don't know specifics