I shoot my Steyr and TX 200 overarm -- bit old school these days but I find it much more stable than off the knee.
Off the knee I find lots of lateral left to right movement - I cant keep the thing still horizontally. Overarm I find the pulse in my arm bouncing the rifle up and down slightly - I try to pull trigger on the lowest part of pulse "bounce".
Having said that I do shoot off the knee for steep downhill angled shots.
Try both positions aiming youir cross hairs at a small target - I use a nail head on my garden shed. You will see what I mean hopefully.