I'm sorry for the confusion, it's just that sometime in the future I might try to get a P. muticus and wanted to find out what would be a suitable enclosure size if it turns out to be a female.Should the 20 long, be 30 inches long or 20 inches long? And what is the current size of your P. muticus?
P. muticus can be fairly large & they like to dig, so they need a good depth of substrate. But even if fully grown, then 30 X 12 X12 is going to be huge. If it's 20 X 12 X12, then if fully grown or close to, that is the size I would go for & I would put a good 6 inches of substrate in there for it.