Caves For Kribs

I'm planning to get some more caves to put in my tank for when I get kribs. What sort of size should I be looking at?

I've got one that is 4x5x6cm (external dimensions). But it's occurred to me that this might be a bit small.

I've also got a couple half coconut shells, which are perhaps 10cm diameter.

Thanks @hampalong

I think I'm going to use coconut shells to provide cave shapes, that I'll cover with plants that coordinate with the rest of my planted tank decor. 😀

Nice one!!!