Thanks for your help, it seems that there were two things holding me up (if anyone else is in the same boat).
HTTP health checks were enabled and not configured so it seems pfSense was detecting my backends as offline therefore not pointing anything through. Second thing was my firewall rule for this was completely wrong and should be as @johnpoz has indicated.
Now that I am able to point frontend to back for HTTP traffic, what is the ideal method for setting this up for multiple custom ports?
The schenario would be as follows:
sub1.domain.com-> 10.0.0.1 (ports 20, 30)
sub1.domain.com-> 10.0.0.2 (ports 20, 31) *note this has a service running on port 31
I setup some port alias's for each, however it seems that the HAProxy package won't acknowledge the input of alias's.
My thinking in doing so was that in some cases, multiple hosts might have the same services running on the same ports, but different hosts.
So then, I assume there would be some manual setup for each host, is that correct?
If so, is it as simple as adding these additional ports to each backends?
Thanks for your help @johnpoz much appeciated.