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Edited with my calculation:

23 actions per sherd, 28 sherds total, 28 actions for labyrinth, 48-48-48-52 actions for court, 14 actions at zee per trip, 49 nightwhispers turned in at ratket at 82.5 echoes each.

82.5x49 = 4042.5 echoes + 132 echoes if we count zailing as 3 epa

23x28 + 28 + 56 + 49x4 = 924 actions

4174.5รท924 = 4.5 epa

This doesn't account for exhaustion so be careful! I only did this for a good estimate.

Clay arm would improve this.

Theoretically clearing the high persuasive check would improve this, but that is impossible for an average player and nearly impossible even if you spent fate. (This would achieve 5 epa)

Favours to tribute is more efficient and it also produces night whispers so this wouldn't benefit anyone but a somewhat patient mid game player. Still a decent grind if you are lacking nightwhispers for ratket