When we first started playing this, Dusty was reluctant to leave the spot where she was first rewarded. I now leave a pile of treats at several locations, and go past a couple of these on our way to the reward spot.
We have started to do it with behaviours other than a sit. And we've extended the sit into a slight stay once she understood the game, by waiting a moment before clicking, and/or a moment after clicking before giving a release and going to get the treat. We'll continue to build duration.