As per my understanding ReservedXcmpWeight seems to be more of a cap in how much weight one block will be able to be filled by XCMP message execution than anything else. Meaning that if no messages need to be served/executed for block X, then all that available block space is there to be filled by other executions.

Notice that there is a similar set up for DMP messages.

I would recommend reading service_xcmp_queue documentation..

As per my understanding ReservedXcmpWeight seems to be more of a cap in how much weight one block will be able to be filled by XCMP message execution than anything else. Meaning that if no messages need to be served/executed for block X, then all that available block space is there to be filled by other executions.

Notice that there is a similar set up for DMP messages.

I would recommend reading service_xcmp_queue documentation for some more insight on, and I quote:

Service the incoming XCMP message queue attempting to execute up to max_weight execution weight of messages