There is no such thing as wake on WAN. wake on lan is a special broadcast message it does not use ports or ip addresses.
What you are trying to do is use a hack that does not work on most routers. Way to many people have written stupid guides and I suspect the never actually used their "wake on WAN" solution long term.
The problem is not the port forwarding. The problem is the ARP entry in the router will time out. You need a router that can set static ARP entries which is very rare. These so called guides do not even mention this issue, but then again nobody would read their guide if they said most people can not make it work because it is missing this required feature.
Just use the sleep options so you can remotely access...