All blends that need to occur above the waist can use the same slot and Layered Blend per Bone…this setup uses over 60 upper body montages:
The layered setup uses Spine_01 in the layered blend per bone node as seen in the bottom corner. If you change the montage for the shooting anim to your Upperbody slot the shooting montage should play normally like the reload without the need for the second layered blend node.