On the F5 you just need to change it from AutoMap to None as per instruction below:
'to disable SNAT for them use: Access Policy ›› Network Access : Network Access List ›› >> Network Settings: SNAT Pool to None'
But from the routing side you need to make sure that the subnet/IP range you allocate for VPN-Pool is reachable from you network.
If I would like to use my 2x arm deployment as an example:
Subnet1 (10.1.1.0/24) - Internal;
Subnet2 (10.2.2.0/24) - External;
Subnet3 (192.168.1.0/24)- VPN-Pool;
On the router in you network a route is required saying to get to Subnet3 (VPN-Pool) go via self-IP (or floating self-IP if you have a F5 cluster configure) of the F5 Internal VLAN
ip route 192.168.1.0 255.255.255.0 10.1.1.252 (where 10.1.1.252 is the F5 floating self-IP)
That was really it. You don't need to do anything else.
As many said previously it all depends on your network and infrastructure but you should get a general idea - F5 is a router on it's own.