Abilities like Excogitation, Lustrate, Indomitability, Tetragrammaton, Essential Dignity, etc. are not affected by statuses that boost healing magic potency (e.g., Convalescence, Largesse, Fey Illumination, Mantra, Defiance, etc.) because they aren't spells. So it doesn't matter at what point Excog's healing potency is calculated because it will always be the same.

They are also unaffected by statuses that reduce healing magic potency (like Infirmity).