Please try to wiced_bt_mesh_core_adv_tx_power=4 is for max power.
You can set this inside mesh_app_init(). Default value is 4. 0 means minimum power and 4 is the max.
"10 meters between node in order the mesh to work properly" -> What is your testing strategy? Is your device responding with a delay?
If the distance between two nodes are high, then we should expect high latency. And congestion due to other BLE (or wireless) device can also affect the performance.
Many thanks ! I've found the setting per your recommendation !