Hi Ralf,
I guess the reason is that the ICI is handled by own HTTP handler (CL_ICI_HTTP_SOAPDISPATCHER) and XMLs are not stored in CRM database. These messages are real-time synchronous messages and they are immediatelly processed. Only when you setup ICI trace level on user level, XMLs are stored in CRM_ICI_TRACE.
The SXMB_MONI is rather intended for data exchange with PI or other exchange brokers, data are stored in SXM* tables. I think proxies for data exchange has to implement different interfaces.
Regards,
Dawood.