If I'm descending slowly with a relatively nose-high attitude - say,
in preparation for a short field landing - does the high angle of the
pitot tube have any effect on indicated airspeed? (I suppose all
designs are different - say this is a 172.)

First, descending or climbing is irrelevant. Only your airspeed
affects the RW.

Second, according to the most authoritative sources, the static source
is the primary culprit behind the difference between IAS and CAS. The
pitot is very accurate until AOA's much greater than our little
aircraft can achieve. I know that popular literature suggests
otherwise.