Hi,
I've notice something odd. When I move the boolean above the bevel in the modifier stack, the bevel changes width. Looking for a second opinion on why this might be happening. 
I haven't taken that course yet but modifier stack order is quite important on most modeling topics. I would think that the boolean is creating geometry that is difficult to bevel so if bevel is below you won't get the same effect because Blender has modified the original mesh data geometry to something entirely different for the bevel to work with. It's is probably clamping the overlap or the area of bevel is being affected.
I think that makes sense. The first thing in the modifier stack that modifies your mesh data will affect the other modifiers drastically since they are working with a modified set of mesh data rather than the base mesh data. In a way this is actually the beautiful power behind modifiers. It's all non-destructive and you can swap the order of things to get certain behavior.
Maybe I am way off here though.
Hey there! Like Shawn had already mentioned, the order of your modifier stack is important since it determines the order which these modifiers operate on your mesh. By moving your Boolean underneath the Bevel, you are indicating to Blender that you want to bevel everything first, THEN cut into the beveled mesh. I personally would try and stick to keeping your Boolean modifiers towards the top of your stack in most instances, since it has a direct and significant impact on your immediate mesh. However, you may find times when you may want to deviate from that!
As for exactly "why" it is producing a smaller bevel when moved: no idea... Would likely have to be something that goes on behind the scenes with how Blender handles the Bevel modifier and how it calculates the faces/edges/vertices of the mesh to determine bevel weights. Like I show in the video, if you move your "cutter" object around you can kind of finagle the bevel amount to fit something that you find more appealing. :)