The Bitcoin rainbow chart popularized log-regression bands. Applying the same construction to Zcash is harsher: ZEC spent 2018 to 2024 in a long decline, so its regression slope is shaped by a much deeper drawdown than Bitcoin ever printed at comparable age, followed by the violent 2025-2026 repricing.
The mechanics are identical: log price, log time, equal bands. What differs is the story the fit absorbs. Bitcoin's rainbow was drawn through a series of higher cycles; Zcash's is drawn through a crash and a resurrection, which makes its bands wider and its fair-value line more sensitive to new data.