There definitely can be an issue with small gecko, big viv when they're young. Admittedly, when I first got my little guy at ~3.5 grams, I put him right into a 12x12x18 exo terra. I crammed that sucker with plenty of fake plants and cork wood (I mean plenty). I was worried he wouldn't find his CGD, but I started finding poops after only a few days. Not a bad settle-in for a Petsmart pick-up!
All in all, I find you can remedy the big world, small gecko tendency by providing plenty of foliage and shelter. If it has sufficient hiding spots and a clear food source, too large won't be an issue.
One thing though, because he's still so small and young in a comparatively large viv, whenever I feed him live it's always outside his enclosure in a smaller critter keeper. Larger, well set-up vivs leave lots of places for feeder insects to hide. I think it's just better to avoid the work of fishing out dead insects.