And as mentioned before, tapering the fins in thickness from
root to tip helps to maximize the cooling and minimize the
weight too.
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It's not just a 'nice-to-have' feature, the draft or taper is an
absolute necessity, first for successful casting, then for EFFICIENT
cooling. Transfer of heat to the atmosphere causes the air to
expand. If the air channels are not tapered the 'fatter' air quickly
REDUCES air-flow through the fins and the engine begins to overheat.

-Bob