Is bag height determined by body size? I thought it would be determined by how high the bipod is set, and the distance from the bottom of the stock to the ground needed to make the rifle point at the target? I am now confused about what to order.
Your bag should be slightly malleable. Any bag should offer enough flexibility to get you between bipod notches, including mine.
If you often find that, because of your large body type, you cannot get low enough to properly engage the rear of your rifle and you often run with your bipod legs extended even when not shooting uphill, you may need a taller bag.
The Answer works for 95% of shooters under 90% of conditions.
The exceptions are:
Not enough bipod leg when shooting uphill and you have to get lower in the rear - Shorter rear bag. (Compromise)
Small, slender body type - Possibly a shorter rear bag but only your experience will tell.
Large body type and you usually run your bipod legs long to accommodate that - Tall rear bag.
Bipod legs are collapsed and you are "floating" your rear bag - Taller rear bag. OR ditch the short bipod.
The malleability of the bag makes the exact height of the bag while in use hard to pin down because of the variable in grip of the bag.
These bags are meant to be gorilla-gripped, firming them for consistency from shot to shot so you don't have to "gather some bag" for the next shot. My students at our courses just run the bolt with no need to rebuild the position.
Shooters abandon their old bags when they shoot mine. Even long-time, experienced shooters. The Answer is always more consistent. At the end of this CA course, all shooters had the Answer bag and one larger shooter owned one and loved it, but needed something taller for level shooting in the prone.
A MAJOR CONSIDERATION -
Many shooters now have Arca Swiss rails and don't "need them". Competitors move the bipod fore and aft to meet barriers and props.
Arca needs an adapter to your bipod to attach with the rail. This moves the apex of your triangle of stability LOWER and your position HIGHER. That requires the bipod to be collapsed shorter. A narrow base of stability is always less stability. A pic rail mounted to a chassis will mount the bipod slightly higher, getting the barrel inside the triangle of stability.
***Photo of Triangle of Stability below but let's not make this thread about bipods, please. Just recognize what it is and get your barrel inside it if you can, otherwise you are teetering atop the triangle.
Thanks.
---Taylor