NAT public ip to private ip

hi hello there,

i have questing about NAT, i have public ip x.x.x.x/28 and y.y.y.y/29. and i want some of the public ip is NAT to my private ip. for example i want to x.x.x.5 NAT to 192.168.100.50 or y.y.y.5 NAT to 192.168.100.51. and maybe add some port forwarding so service in that server can expose to internet, let say port 2222 from public ip forward to port 22 private ip.

currently i have configure my fortigate with this, but still no luck

and i realise that, i have /28 public ip. but only 1 ip that i can ping from internet, the one that i can ping is my public ip in interface wan1, why the rest of 13 public ip cannot ping from internet ?

cus i have experience with mikrotik and i can do ping to all my 14 ip subnet /28.

anyone can help me?