The tube may be too steep for him to climb, if you can lower the shelf & just remove the tube he should manage ok getting to it from the floor or you could get a bendy bridge & use that as a ramp for him to climb up.
The house should not be on a shelf but on the substrate in the base. That house doesn't look very suitable for a syrian tbh, I would just use a cardboard box, no base & a hole cut out for a door, the house needs to be dark inside & plastic houses can get a bit damp with condensation too.
What substrate do you have there? It doesn't look like a suitable hamster substrate that he can dig & burrow & nest in.
You really need something like kiln dried pine wood shavings,
carefresh or other paper based substrate or you can use
hemp. A nice deep layer, the base of your cage looks as though it may be a little shallow but basically get as much in as you can.
Your cage really isn't ideal for a Syrian hamster, you might want to think about getting a better cage for him,
Zooplus do a few good cages, there's the hamster heaven which is a little small but still ok although best used without the tubes & penhouse (the cage comes with blockers for the holes), the alexander which is a great cage or the alaska which is also a good cage although quite high so it's best to put some shelves or levels in for safety.