USG Flex 500: WAN failover and virtual server won't work

Hello everybody

I have an USG Flex 500 with 2 wan and 2 lan connected, and i'm trying to make a server inside a wan to respond to two NAT (Virtualserver), one on each wan.

I should use virtualserver NAT because i need to redirect different ports on same external IP to different internal servers.

This is the simplified layout of my network configuration that causes the problem:

USG Flex 500 configuration:

Interfaces:
LAN1: 192.168.1.1/24
LAN2: 192.168.2.1/24
WAN1: 1.1.1.2/29 GW 1.1.1.1 (Connectivity Check enabled)
WAN1.1: 1.1.1.3/29
WAN2: 2.2.2.2/30 GW 2.2.2.1 (Connectivity Check enabled)

Policy route:
1: LAN1 to ANY, Next-hop: WAN1 SNAT: outgoing-interface (1.1.1.2)
2: LAN1 to ANY, Next-hop: WAN2 SNAT: outgoing-interface (2.2.2.2)
3: LAN2 to ANY, Next-hop: WAN2 SNAT: outgoing-interface (2.2.2.2)
4: LAN2 to ANY, Next-hop: WAN1 SNAT: WAN11_ADDRESS (1.1.1.3)

NAT:
1: VirtualServer, Interface: WAN2, src: any; External IP: WAN2_ADDRESS; Internal IP: 192.168.2.5, Port 80
2: VirtualServer, Interface: WAN1, src: any; External IP: WAN11_ADDRESS; Internal IP: 192.168.2.5, Port 80

Security policy:
1: From LAN1 to ANY: permit
2: From LAN2 to ANY: permit
3: From WAN1 to ANY: permit (just for the test...)
4: From WAN2 to ANY: permit (just for the test...)

Now,
if I navigate from internet to http://2.2.2.2, 192.168.2.5 serves the page successfully
if I navigate from internet to http://1.1.1.3, responses from 192.168.2.5 comes out from the wrong WAN because of policy route 3: If I enable logging to security policies, i see everything permitted and with tcpdump on 192.168.2.5 I see the incoming request.

I have tried using trunks but in this case i cannot configure policy route 4 to use an IP different from WAN1_ADDRESS

How can I make the server to respond to both addresses while each WAN act as failover for the other?

Thank you