I have found over the years that solid is a must for long range. This is even more so past 1000. It all started while I was in the midwest and was shooting prone off some wet soggy pasture one day. My bipod was getting a little deeper with each shot. My groups were noticably larger that day. Later it showed up again with a horrid group when I rested my rear bag on top of a shooting mat. Removing the mat tighten things up a lot especially in vertical. Since then I have played with this a bit and have found this to be a huge help to me, especially at ELR. I do these things, once prone I take my left hand and grab the bipod legs and scratch them into the dirt to get them on solid ground. I only use a dense rear bag and set up to be low on the target and work the rifle butt down to be as solid as possible. You won't find any sort of mat or padding under my rifle or bags. I want them solid as can be in the dirt. From this point I ever so slightly pre-load the bipod forward just a bit, just enough so I can feel the recoil pad on top my shoulder. Then I check my cheekweld like you would with your anchor point on a bow. I have found that when all is right I can feel it is and becomes a confident feel for me with consistant practice.
Another point along this line is that while attending the Defensive Edge long range class Shawn made it known he is very fond of pod locks. I think this is also to keep things solid durring recoil.
One of my shooting buddies, "Montana Marine" has been using the aid of a monopod on the rear of his stock to stiffen things up. He shared with me at our last long range shoot that it has noticably reduced vertical spread for him.
So, I just wanted to pass this along. Take it or leave it. But for me I can not get things solid enough and the more rock solid the better.
Jeff