Glad he has settled down
70cm is way too tall for a hamster cage. They can fall between shelves if they monkey bar across the roof (and we don't see what they do in the middle of the night) and aren't good at grabbing onto things so it could be a long drop or bouncing off the edge of the shelf and they can get injured. You could put a full level in maybe as that's the only real way to make a tall cage safe, but it would mean a bit of diy.
Where did you get the cage? Some people have had success asking for a refund and taking it back after a new, more suitable, cage has arrived. If you haven't had him long there's a good chance of trying - just say it's not suitable and too tall for your hamster. Depends where you got it from possibly.
If you do manage to, then the Alaska cage from Zooplus is very reasonable at about £33 and is a good cage for a Syrian, without needing add-on bins and cages. Although with you mentioning 360 square inches I'm guessing you might be in the US? In which case it might be better to just make one large enough bin cage rather than an add-on bin.
Re: New hamster breathing super fast and in corner all the time??
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