Is this the same snake?? If so, he is definitely not trying to eat. The snake in this post is stressed. The exploring is a sign of stress. A comfortable ball will stay in their hide most of the time, sometimes coming out at night to look around a bit. When he stayed in his hide in the smaller space, he was feeling more secure.
If this is the same snake, I would suggest putting him back in the smaller container, leaving him for a week, then trying to feed him again, once he is acting more comfortable. Once he is eating reliably, then you can try to use the bigger tank again.
Whereas in the wild they do get more than 20g, they don't often leave the termite hills they live in. It's possible to use a tank that large, but keeping the temps and humidity in the correct ranges is not only going to be hard, it's going to be expensive. Your also going to need a ton of stuff to clutter the tank so your bp doesn't get so stressed. Personally I would give up on the huge tank until he is eating well at least.