IDOC-> XI -> IDOC connection issue

I am trying to do a simple IDOC to XI to IDOC scenario. I am trying to pass the IDOC to XI through an RFC destination of type 'H' (HTTP connection to R/3 System). The sending system is an 6.20 system. I think my problem is in setting up this RFC, I believe I have WE20 and WE21 (using XML HTTP port) setup correct. When I try the IDOC, it errors out before getting into XI. I have SICF active (/sap/bc/ and /xi/ ).

Can anyone tell me what step(s) I may be missing? What pathprefix in SM59 should the RFC be pointing to on XI for XI to receive the IDOC? Is there something that needs to be setup on XI to receive this IDOC?

Thanks for any guidance,

Jake