For this type of measurement, “zero span” would be the best place. Just set your IF bandwidth to your channel bandwidth, with the signal centered.
If it is a constant amplitude envelope (e.g. FSK, GMSK), a marker anywhere gives you channel power. If not, you could export the zero span data into a CSV, and then (in mW units, not dBm) average the power of each sample within your packet.
I’ll talk to AJ and see if this is something we could add to the next release.