Hello.
I haven't heard about this kind of limit, but maybe SAP people know some secret parameters.
However I know that MaxCallsInQueue is a custom parameter for custom IVR, so this isn't a setting you are looking for. This parameter is used in BCM Conditional IVR sample.
If there isn't this kind of setting, my best guess would be query current contact number with python from Monitoring database TAMCurrentContactList table and create max calls check to the beginning of the IVR.