The split between C12 and C13 follows the end underside, not a fixed level: C12 rows lie between the Level underside and
the end underside (taper height h2), C13 rows between the end underside and the top (end height h1). The break is the end
underside + 127 mm, the taper line's start at the end face. P1 is unchanged (C12 41.288–42.288, C13 42.538–42.788). Tests
check the band rule for h1 and h2 changes.
Co-Authored-By: Claude Haiku 5.5 <noreply@anthropic.com>