Let's put it this way. In the wild, a burrowing spider would have more or less just enough space for itself in the burrow. I think you're thinking that the space isn't enough because it wouldn't be able to molt. Again, in the wild, a t wouldn't go outside of its burrow to molt. Think about it. If the t got out of it's burrow and sat on open ground for hours while showing off it's most vulnerable side, wouldn't that be more dangerous than molting in a tight space? It would feel much more secure in a tight space since it would be able to feel all the vibrations around it. I've also seen them molt in their burrows and if it's too small, tey could just fold their legs. And ts spend most of their time in burrows or hidnig spots. They don't actively hunt food. They're opportunistic. They just need a home.depth wise perhaps but a 3 inch spider in a 4 inch diameter container? idk.
And in a tight container, the t could think that its entire container is its burrow.