Electric Blanket and Mattress Topper

My mattress topper is like a puffy duvet, secures to the mattress on the corners and lies flat under the sheet. I now want to use my fitted electric underblanket but can I use both the topper and electric blanket at the same time? Which goes at the top and which goes to the bottom? If I use the electric blanket at the bottom, will the heating come through? Or if I use the electric blanket at the top, it won't be able to secure it to my mattress.