i dont think it matters your using ipsec..
When using transparent-client-ip feature ALL reply traffic from the webserver:port is redirected to the pfsense system ip-stack for haproxy to pick up..
This also happens when accessing a server on opt1 from the lan-network..
It is a limitation of the ipfw & pf firewall combination required to make transparent-client-ip work..
Workaround might be to portforward incoming requests over ipsec or other to haproxy.
Its a known issue, also in the warning/explanation near the transparent-client-ip setting, however to get it solved a patch to pf is needed.. https://redmine.pfsense.org/issues/3943 . Not sure if/when that will get applied..