Hi and welcome
. Robos are great tunnellers! Five days isn’t long so he’s probably still hiding away a bit. On the plus side as they grow in confidence they are often out more than Syrians - during the day eg.
I had one and he was very much a look don’t touch pet. I didn’t really try hard enough to tame him at the time so he never was fully hand tame abd would always hide if I tried to get him out. But - he did learn to know and trust me snd would sit for quite long chats! Him in his cage - me outside the cage with the door open. But if I put my hand in he was off. When he was older it was easier to get him out as I had a cosy fleece cube he liked and would walk into if I put it near his house so lifted him out that way.
I felt like you did at first snd I actually reduced the depth of substrate in the end - it did no harm as he just built a mountain of it under the shelf and had a burrow in that instead.
Plenty of hidey places in the cage helps and they will move from one to another so under cover. They also don’t like feeling too exposed from the top which makes them hide away as well. Difficult to have shelves and hanging things in a tank but some larger tunnels work quite well - like the large cork logs - it’s like a kind of overhead shelter. They do also seem to really like a shelf or platform both to hide under and climb onto. Somehow they feel less nervous of going into a platform than being out in the open on a substrate. I had the sand bath on the platform so he would go up there because he LOVED his sand bath!
Just keep talking to him do he gets to know your voice - even if you don’t see him.
Also two wheels can help - a normal wheel and a flying saucer. Our Robo used both but he LOVED his saucer!
It can take two weeks for them to fully settle in a new cage so time and patience. Would love to see a photo when he emerges!
Also if you have a photo of your tank set up we can maybe suggest the odd tweak but it sounds like you’ve thought of everything.