the designs are nice to compare as they are the opposite extremes
max fins close-coupled to no fins at all
both bps are thick, the 462-U is 0.31in. and I would guess the Innovatek to be something similar
- but no way to measure other than estimating from that old THG image
my suspicion is that:
in the Innovatek the higher flow is passing through the upper fin (disk) area where it is of little benefit
whereas
in the 462-U the higher flow contributes directly to "better cooling" (a lower thermal impedance) via the improved convection rate
- hence also its relatively poor low flow rate performance
to return to your question:
don't think that spreading resistance accounts for the principal differences between these two
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