26000/27000 feet for what Shaka Zulu, Vmo/Mmo, Max Rate Climb, Econ Climb, Best Angle Climb, Maximum Range Cruise, Long Range Cruise, Nominal Descent Mach/CAS, High Speed Descent Mach/CAS, One Engine Inop Drift-Down? - Changeover Pressure Height varies for each CAS/Mach schedule. I know of one aircraft type where there is about 20000 feet difference between 2 of these schedules I've mentioned, and know of no aeroplane where CAS rules below a particular Pressure Height and Mach Number above, except for a specific CAS/Mach schedule.
Can you be specific?