I think they're hard to relocate on purpose.

The SO is actually saved within the containing PSD, not linked from it, so editing the file itself without using the "Edit smart object" feature won't cause updates elsewhere. Since these are temporary files, storing them in a system temp folder seems appropriate so that they can be automatically cleaned out from time to time.

If you want to write a copy of a smart object out to disk anywhere you like, right-click it and choose "Export contents."

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Walter Soyka