Pass the fade factor to mbl.get_z

Marlin/mesh_bed_leveling.h

       return z1 + delta_a * delta_z;
     }
 
-    float get_z(float x0, float y0) {
+    float get_z(const float &x0, const float &y0
+      #if ENABLED(ENABLE_LEVELING_FADE_HEIGHT)
+        , const float &factor
+      #endif
+    ) const {
       int8_t cx = cell_index_x(x0),
              cy = cell_index_y(y0);
       if (cx < 0 || cy < 0) return z_offset;
       float z0 = calc_z0(y0,
                          get_probe_y(cy), z1,
                          get_probe_y(cy + 1), z2);
-      return z0 + z_offset;
+
+      #if ENABLED(ENABLE_LEVELING_FADE_HEIGHT)
+        return z0 * factor + z_offset;
+      #else
+        return z0 + z_offset;
+      #endif
     }
   };
 

Marlin/planner.cpp

     #if ENABLED(MESH_BED_LEVELING)
 
       if (mbl.active())
-        lz += mbl.get_z(RAW_X_POSITION(lx), RAW_Y_POSITION(ly)) * z_fade_factor;
+        lz += mbl.get_z(RAW_X_POSITION(lx), RAW_Y_POSITION(ly), z_fade_factor);
 
     #elif ABL_PLANAR
 
 
       if (mbl.active()) {
         #if ENABLED(ENABLE_LEVELING_FADE_HEIGHT)
-          const float c = mbl.get_z(RAW_X_POSITION(logical[X_AXIS]), RAW_Y_POSITION(logical[Y_AXIS]));
+          const float c = mbl.get_z(RAW_X_POSITION(logical[X_AXIS]), RAW_Y_POSITION(logical[Y_AXIS]), 1.0);
           logical[Z_AXIS] = (z_fade_height * (RAW_Z_POSITION(logical[Z_AXIS]) - c)) / (z_fade_height - c);
         #else
           logical[Z_AXIS] -= mbl.get_z(RAW_X_POSITION(logical[X_AXIS]), RAW_Y_POSITION(logical[Y_AXIS]));