I did that too, with the fleece on top, until I realized the bottom was fairly well protected. Also "they" are usually interested in large metal objects. Plus, BP on top is handier for bopping rude/drunken passengers on the head.
Yet another advantage of having the backplate on top is that if the airline agent says my bag is overweight, my plan is to pull out the backplate and strap it on my back to wear onto the plane. Easier than rummaging around for several smaller items heavy enough to make a difference.