GGB The Islamic calendar is lunar, so Ramadan arrives roughly ten to eleven days earlier each Gregorian year and moves steadily through the seasons. That drift changes its commercial effect: falling in the winter peak it reshapes your strongest months, falling in summer it overlaps the trough. A seasonality map therefore has to be redrawn every year, not copied from the last one.
From Ramadan and the Seasonality Map: Revenue Planning for GCC Restaurants — the full reading, with the method behind this answer.