I keep my Lasiodora spec. (suspect it's a parahybana, so same size roughly) in a terrarium of 40x50x30 cm, 30 cm being the hight and about 10 cm of that substrate. i can only say that she uses all of the space and even rests in different corners of the tank. she doesn't use her hide but she loves the pieces of wood and plastic plant i put in that she can lurk behind. for a species of that size and taking into account their defensive and sometimes agressive behaviour, i wouldn't choose a much smaller tank for them. more safety distance for your fingers !
Truthfully I keep all mine in 20 qt Sterlite bins. They seem to be doing just fine. If they seem crowded I wouldn't see it necessary to move them into anything larger than a 10 gallon tank about half filled with substrate. Just remeber, a well fed T is not going to be cruising around the tank so huge amounts of space are not really needed.
We don't go with anything bigger than a 10 gallon aquarium. I worry to much about them finding their food in anything bigger.
So, how is your difficlis? How is it temperment? I'm curious, mine is still a tiny sling.
it's about 3 inch long - nice temperment - nervous, rins away and hides alot, but if undestrubed you can watch it for hours wondering around. When moving it tends to be skitty at first then calms down and moves fairly slowly. Not seen any aggression from him.
Is normally out when hungry - but eats like a pig so is normally always hungry.