Is the public IP, in your case, the IP of your firewall's external interface, or another address from your public IP range?
If it is the IP address of the firewall's interface, no manual ARP entry is required.
...but you still need to add another rule below yours, to ensure that the responses from Original Service 443 are translated to Service 8443.
If it is another address from the same public network, in addition to these two rules, you'll need manual ARP.
To do that, in Global Properties | NAT, check "Merge manual proxy ARP configuration"; OK
Publish changes and install the policy.
After policy is installed, SSH into the gateway and execute following commands:
add arp proxy ipv4-address AAA.AAA.AAA.AAA interface ethX real-ipv4-address XXX.XXX.XXX.XXX
save config
Where AAA.AAA.AAA.AAA is the public IP address you are using for that host, ethX is your External Interface and XXX.XXX.XXX.XXX is the IP address assigned to your External Interface.