I came across this dramatic photo of how various radiant floor strategies look to a Thermal Imaging camera (NOTE: I found a thermal image of warm board and have included it here as a composite insert. It was taken by a different photographer, using a different camera, but the indicated eveness of the heat distribution is quite interesting):

Staple-Up Construction

Suspended Construction (not touching sub-floor)

Channel Construction

Spreader Plate Construction (note fall-off at edges of plate in IR photo)

Continuous Aluminum Layer Construction
Regards,
-AC_Hacker
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