Cheekpiece is an important place on the rifle. It is important that you can lay your head down on the cheekpiece in same way everytime. And also straight down. The goal with it is that you see straight thrugh the diopter and frontsight. At the same time being relaxed in your neck. To manage this demand a perfectionisme in the placement of the cheekpiece and practise a lot. However, it doesnt stop with that. If the atlethe does not make sure that the buttplate is placed in the same place in the shoulder every time it is hard to place the head in the same place on the cheekpiece everytime. To far down and the cheek will come a bit more closer to the diopter and pressure is different. To high up in the shoulder and the cheek is more back on the cheekpiece and maybe more pressure too. This effect the zero-point and the atlethe think hen is aimining in the middle but reality is different. So the placement in the shoulder and cheekpiece needs a lot of attention and work.