FWIW I hold the rifle in both hands. I rest the back of my weak hand on the rest. I find that this way I get a POI which better reflects what I'll get in the field when shooting from an improvised rest. It seems to give me better accuracy with light rifles than letting the rifle rest directly on the bags and recoil freely too.
I also pay attention to details: buttplate on the shoulder, in the same position each time and with the same pressure, elbows in the same position, rifle "on aim" without muscling (natural point of aim). If the rifle boots a bit I might kneel behind the bench, or use a standing rest, so as to be able to "give" with recoil.
I also try to get there early and shoot in still conditions.
