In G28 Z is sort-of known

Marlin/src/gcode/calibrate/G28.cpp

     if (z_homing_height && (doX || doY || (ENABLED(Z_SAFE_HOMING) && doZ))) {
       // Raise Z before homing any other axes and z is not already high enough (never lower z)
       if (DEBUGGING(LEVELING)) DEBUG_ECHOLNPAIR("Raise Z (before homing) by ", z_homing_height);
-      do_z_clearance(z_homing_height, TEST(axis_known_position, Z_AXIS), DISABLED(UNKNOWN_Z_NO_RAISE));
+      do_z_clearance(z_homing_height, true, DISABLED(UNKNOWN_Z_NO_RAISE));
     }
 
     #if ENABLED(QUICK_HOME)