Don't be afraid to cover those walls! When it comes to crestie cover, I always say the more the merrier. I've found that cresties are more prone to hang out in the open when they're comfortable and given plenty of choices. When they feel safe, they'll become more adventurous and make themselves seen more often.
Just a quick example, I had one viv on a desk with all 4 sides open. This crestie was comparatively more reclusive than my other crestie, who's viv is on a shelf (the shelf blocks the back and side wall of the viv). The crestie on the shelf loves climbing on the visible walls, hanging out on his perches in the open, etc. During the day, he likes lounging on the leaves right in the front in plain view.