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. 🙂
