Most of the laying boxes I use have the holes on top. I have also found that with shoeboxes you can put the hole near one corner and they don't (usually) dump the substrate out, they tend to dig at the opposite corner.
Then again, I have 2 sisters who insist on piling the dirt where they like to lay their eggs, doesn't matter where I think they should put them. In their cage the dirt is likely to end up anywhere no matter where the entrance is.