12-5 just feels a lot more inconsistent since the rewards can vary so much based on RNG for the second half of the map, and I often miss 1 or 2 chests. So if you care more about ampies/triggering gardens 12-3 might be better.

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Now that I'm looking at the map again, I think I'd get the most gold/seeds if I just stacked everyone on the top left node. I might try that to see if it's better.

EDIT: Seems worth it if you can handle having less control over where your squads go and the extra moving pest damage you take by starting further back.

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Stacked all squads in the upper left. One squad died a little early (before hitting the final boss), which lowered the gains a bit.

It helps if your weaker squads are slower so they never fight and can just pick up goodies after your strong squads clear the way (barring bad RNG sending them to the frontlines).