after being forced to watch baseball, I think a diamond shaped pressure sensor would be a good idea for total accuracy for being on the tile. One pad in hte middle of each side. Since the sensor is basically a switch, you need all 4 shut before it will turn on.

Who knew watching baseball would give me a good idea.

Now to fight with PDF generation code at work. Come on c# and .Net ... who's loves you like a red headed step child.