Symptom

Family tier stream cost is much too cheap. The discount is compounded (applied twice) resulting in ~65% off instead of the intended ~44% off.

What you know

FamilyTier extends PremiumTier. Family subscribers should get the premium discount (20%) plus an additional family group discount (30%). The expected cost is baseRate * 0.8 * 0.7 = baseRate * 0.56, but the actual cost is baseRate * 0.35.