I hold all my rifles at or near the entry-pipe when shooting standing/offhand. When testing loads, I usually hold the rifle the same way, resting the back of my left hand on the bags, bags adjusted for proper elevation of the rifle and sights.
If strictly bench-testing loads and not caring where the group lands, I will rest the entry-pipe on the bags and use my left hand to hold the underside of the buttstock, at & against my shoulder, or for squeezing the rear bag if I use one.
When chunk shooting, I found my .40 was most accurate when I rested the lower entry-pipe on the bag that was on the 'chunk'. Resting it further out, at the top rod ferrel, my groups opened up. One must find the most accurate location for his/her own rifle with THEM shooting. It is possible a different shooter will group differently (location and size) with the same gun, same load. It is all about how each person shoots, holds, their eyes as well in how they see the sights. I shoot 2" low with Taylor's rifles when they are sighted for him.