[cypher]

That's not very tall & I do think it's important to have a proper lid on all cages, you just can't know what might happen without one.
Ideally you want at least 15cm of substrate which leaves only a very tiny space between the substrate & top of a cage that size so you might be better finding a different bin that's a fair bit deeper, robos do love to dig & tunnel so the substrate is important so a little less floor space but deeper substrate would be more suitable I think.