Reverse proxy with different default gateway

[schs]

Hi Forum people,
We're looking to replace our TMG 2010 box with pfsense or something else. I'm trying to test this in a semi isolated environment from our prod LAN so we can see if this will fit in with our requirements.

So far i've got pfsense set up with squid reverse proxy in a VM on my machine, with 1 interface on a hyperv external switch to connect to the LAN and 1 interface on a private switch to connect to another VM on my testing machine, I can ping to and from the VM on my machine and the pfsense VM. I can ping between a web server on the LAN and the pfsense VM as well.

from my testing VM i'm not able to load a webpage from the LAN server at all, i've checked the firewall rules on pfsense and traffic is being accepted on the WAN side but doesn't appear to be either passed to the server on the LAN or get passed back.

we have a different default gateway that is not the pfsense box (this can't be changed either as its our core switch), our internet is filtered through a separate firewall as well.

The current TMG box just provides some reverse proxy services (around 10 external DNS names spread over 2 or 3 public IP's) so we are in need of reverse proxy hence installing the squid components in pfsense

is it possible to have a config behave in the same way as TMG 2010 web publishing rules when the gateway is NOT the pfsense machine, or is there another package I need apart from the squid reverse proxy?

i'm pretty sure it's not my hosting machine setup that's causing this, as I had tested it with machines on private switches and it was working, but they didn't have a default gateway configured, so i'm not sure if the different default gateway on our prod servers is causing problems or not