Overall, developers can very subtly tailor the pose to the weapon and uniform.
For soldiers in parachutes, cuirasses and other bulky equipment that they wear on their chest, it is better to adopt a pose in which they hold their weapons at the side, on the shoulder or in their hands, not pressing them to the chest.
The problem with overcoats can be solved by making them fit snugly around the legs. At least that’s what’s on the menu. However, pants also come in different shapes. It is possible to make trousers under a overcoat . . . draw in . . . I don’t know.
The weapon on the back can simply be pointed with the barrel in the direction in which it will not clip with the legs, and the magazines can be turned in the direction in which they will not clip with the body.