No, it would still hit from my testing. The height provided by the pic rail on the IWC mount and the pic connector on the light are greater than the lip of the cap and remaining gap.
Wouldn't it have to be heat treated after the slots were ground in?
If you look at the factory multi position tube you can plainly see what appears to be heat treating at each notch.
I personally wouldn't want to be the guinea pig since the wallop to the face from the recoil of a 3 inch slug or buckshot would likely not be particularly pleasant should the slots peen over or give way due to the recoil.