At Del Rio, Texas (the nominal old stomping ground of Wolfman Jack!) I doubt (could certainly be wrong) you will need to worry much about Winterkill under a cover of dirty ice. (That would be one reason to have a shallow water diffuser, to run by itself and blow a hole through the ice without hurting the deep water 39 deg F "warm" water refuge. But that's a Northern thing.)

Pond shape would also help determine optimum diffuser placement. If it's a simple bowl with one deep spot, I would place them together. If it's oblong or otherwise stretched out, or if there were two deep spots, I would separate them.

"Live like you'll die tomorrow, but manage your grass like you'll live forever."
-S. M. Stirling
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