Seems it's more important to consider the second point of support, as Iin whatever is used to support the rear of the stock. Whether shooting off a bipod or a proper shooting rest bag or a pack, if there's no support besides one's shoulder at the back end, the heartbeat will play a significant role in shot placement. A small 'squeeze bag' seems the best bet in the field. On a bench of course there are even better options, right up to eliminating all contact but touching the trigger... But for less mechanical precision shooting a squeeze bag long enough and with the right kind and quantity of fill is great for providing a flexible, stable rear anchor, virtually eliminating heartbeat or breathing from the equation. Look to some of 260rips videos on YouTube for excellent results derived by its use. Some of his shots go over 500 metres on targets like magpies and rabbits, with very impressive consistency, using a sturdy bipod OR a backpack as the front rest, and a carefully controlled squeeze bag under the rear stock.