Hi Alex,
Good question!
There is in fact an option I added years ago when I realized that the -av value could be approximated by a broad average of interreflection calculations going on, anyway. It’s not super-reliable, but if you set -aw 40 or so with a -ab 1 or -ab 2 calculation, you should see a general raising of indirect values.
This option is turned off by default due to the hazards it presents when computing both indoor and outdoor interreflections at the same time. This causes the interior lighting values to be raised more than they should be. If you are doing everything outdoors or indoors, then there is usually no problem with this option.
Cheers,
-Greg