If that is the case, I would suggest moving to mod_gearman as a remote worker as opposed to Core. mod_gearman works like this:
Nagios (your main server) needs to run a check
It looks to see if the check to be run should be run on a remote worker
If so, it tells the remote worker to run the check, and return the results
The remote worker does so, and Nagios takes back over, creating local performance data files
In your current setup, the main XI machine has no knowledge of the remote machine until there is a passive result sent via NRDP. In the mod_gearman setup, your main XI machine is anticipating an active check result, so the performance data is created as if the XI server itself performed the check.
Take a look at this doc for more info, and let us know if you have any further questions:
https://assets.nagios.com/downloads/nag ... ios_XI.pdf