Actually, I think I have my reactivity backwards. Down and left is more reactive than up or right (on the periodic table). Though Calcium is below Sodium, Sodium is to the left of Calcium. It's been too long since I've done chemistry and ionic bonds, so I can't actually figure it out for sure anymore.

Still, the concentrations are quite different. Soap is also made from lye (or at least used to be), but that's also not the same as oven cleaner though it too works similarly.