Hi Steve!
In this case i would use a clone of the bright version as mask on the bright version itself.
Write the name of the hdrwt version into PixelMath.
Than simply pull the triangle from Pixelmath into the bright version with rescale on.
Than 2 careful MTFs to get the same background brightness, still using the mask gets me
the dark structures into the bright version without the hdrwt artefacts.
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Aloha
Gerald