Tight vs Loose hold on the shoulder when shooting with bipod, no bag?

[jtlassila99]

How do you like to hold a 30+ cal rifle when shooting with bipod and no rear bag?

I did some testing in fading daylight tonite at the 100yds range and experienced what I felt were unexplained misses.

I then tried pulling the rifle to my shoulder with the right arm tight versus not pulling.

   Loose on the shoulder:   Avg dispersion about 3/4 MOA
   Tight on the shoulder:   Avg dispersion about 1/3 MOA or a bit less

Where do you keep your left hand when shooting like this?  I keep it at my Rt shoulder, holding the butt stock.

I only had time for a few shots before it got dark.  In the target picture I numbered the shots and labeled L or T for loose or tight on the shoulder.

With the tight hold, the sight picture was shakier, but I felt like I could call the impacts more accurately.  With loose holds I felt the misses were puzzling.