I used to find our Syrian preferred a bigger house so he could make a big nest in it. They also like it if it's dark inside so putting a bendy bridge over the door can help. Our new baby syrian is doing something similar - he didn't choose the house I put out (it has a hole on top so isn't very dark inside) and is nesting under a shelf and has turned it into a house! By piling up substrate in front of the shelf. He then burrows out and comes up through the house lol.
Our last Syrian also ignored a nice little house I put in, but when I put a bigger one in with a bendy bridge over the door he moved straight into it. You could try a shoebox house - cut the bottom out of a shoe box and a hole in the front long side for a door and keep the lid as a lift-off roof so you can check inside. And put a bendy bridge over the door and see if your hammy moves in. Some of them do have quirks though
