Sorry, but I think we might be talking past each other.
I don't think now that you are looking for static nat. With this feature you are dedicating a single ip address on the public side to a single ip address on the private side. It cannot be used then for any other server or purpose. Thus the concept of only forwarding certain port is not in the configuration. You are dedicating the public ip to that private ip for all ports.
Where you apply the restrictions is in the security policy. Only those ports with a security permit policy configured will actually reach the private server address.
The port configuration you see for static nat is if you need to translate the port in addition to the ip address, changing 443 to 8080 for example.
If you are looking to share an ip address and send three ports to one server and other ports to other servers then you would need to configure destination nat for the inbound traffic and source nat if the server initiates outbound traffic on that port. If all the traffic is inbound no source nat policy is needed as it will match the existing session.