I've made several OBWs, but didn't need the mirrors for those. The OBWs got me interested in kaleidoscope quilts in general. I've only made one small 4patch posey, but plan to do one with more wedges. I have the fabric, but it has large-ish areas that are plain background that I want to avoid. You probably can get away with a smaller size. You can see quite a bit of the fabric by looking at it from different angles (you move, not the mirrors). I used the 12" size because the only other pre cut mirrors I could find had beveled edges. The other thing I did was to cut wedges of chip board at a couple of different angles so I could precisely position the mirrors for 4, 6 or 8 wedges.