I think it is a good idea use a standing rest to regulate a double rifle or light sporter. One should try to replicate a hunting shot as best as possible. I have had many rifles group differently and shoot to a different zero if benched.

I constructed a portable table with an adjustable wooden crossbar to support my left wrist. It is best to find a comfortable offhand position, and have the rest brought up to your position. The upright position is certainly of benefit with a heavy.