Node yields assume the base harvest HP from game data (e.g. 1000 for Redwood trees, 620 for Metal nodes). In-game, trees and rocks with bAllowHarvestHealthScaling have per-instance HP that varies with the node's size, so actual yields per node will vary. The values shown represent the average.
The Megachelon is the best Leech Blood farmer with a 1.25x gather multiplier from game data. The Moschops is the runner-up with 1.25x.