Question Combine aim animation with normal ones

Hi guys, after inserting the basic animations for my character, now I'm trying to figure out how to combine these animations with the one to aim.
From what I understand about they must use Layers in the animator controller. I tried to create a new layer in the animator, inserting an avatar mask with a skeleton. On the avatar I deactivated all the limbs except the arms and the head (because while I aim, I would like these to change the position and "hook" to the basic animations). Finally I added in the layer the aim animation to test.
The result is that if I set the two layers both "Override" the character is affected by both and even if he raises his arms to aim, the normal animations they are ruined because also the torso and the legs are affected (even if I in the target avater, I disabled them).
If I set the aim layer to "additive" the aiming animation does not affect anything even if I set "Weight" to 1 the arms don't even lift.
Both on "additive" the character sinks into the ground.

Can anyone help me and explain how to do it? I just wish that when he aims, his arms it changes animation.

Maybe I have to use a single avatar for both the avatar mask and the animations? because the animations don't all use the same avatar, I took them from mixamo and sometimes I created different avatars for each animation.