I think the problem indoors is lack of humidity in the air, mine gets about 5 hours direct sun at least in the summer when the sun is high. Doesn't get much or nothing in the winter months..
It is planted against a wall and does not get much rain, I think once established it is drought tolerant.
Direct sun behind glass is different from direct sun outside too, so maybe that's why they say to keep it out of direct sun..
Lack of humidity could be handled indoors by putting the pot on a larger bed of pebbles with a layer of water but the water not touching the bottom of the pot, it will increase the humidity around the plant.
In the winter I would put it in the coolest but well-lit room you have..
