I think you'll be fine then ! Now it is just a matter of selection, if your slave router is still visible when far away.
One problem is that the ESP-07 has a built-in ceramic antenna and it is on the top edge of the module between pins 1 and 16.
Depending on the orientation of the plastic box it is inside the antenna lobe may or may not find the router's antenna.
I thought the ESP-07 has an external antenna connection point ? and a plastic box will hardly hamper your connection.