Today, finally, after six months I freed my larger plant from its plastic bag. Since I've gotten it, it has lost about 50% of its foliage and shown pretty much no improvement. In the hopes that this will help it, I've cut away the bag and will just spray the leaves several times a day.
Interestingly, when I picked up the pot the roots were trying to climb out of the bottom of the pot. When I first planted it, the root ball filled about a third of the pot. That's quite a bit of root growth for zero foliage growth. Maybe that's where all its energy went?