Help with understanding animation layers, masks & IK

Hi all, I have a model which I have created a controller for and am using the root motion and IK on. I have a bool for running and one for shooting, which transistion from idle to each animation. everything works great.

But, in order to make this work properly, I need to split the torso and legs so that the player can shoot from either idle or running.

So, I created a mask for legs only and one for torso only (with IK unticked on both).

Now, I put the idle animation on the root and put running on the legs layer with a weight of 1 and I put shooting on the torso layer with a weight of 1.

Now, when I move the player shoots around the scene like a lunatic, like hes moving 50 times faster than he should

I thought it might be IK, so I enabled this in the foot mask, but then the character is stuck to the floor and doesn't move.

If I put it all on the base layer, it works fine as it should.

I really don't understand whats going on, and I cant find any decent documentation or tutorials on animation layers, masks and IK.

Please can someone help me?