Location is patio, about 5 hours of sunlight in the morning through screen, and indirect light for the rest of the day. If I don't water it, it stays in stasis. No growth, just treading water. If I water it, immediate defoliation the next day.
OK I can only tell you what I do with my ficus and how they respond.
Mine are currently in a basement under lights because its too cold up here outside for them. So they arent getting as much sun and wind blowing around as yours is.
Sun and wind will tend to dry out the soil faster than a tree inside under lights
They are in similar soil to yours, large particle, free draining.
They get watered every other day sometimes every day and all their leaves are dark green, not curled and not falling off them.
The curled leaves, and the fact you say they turn yellow and drop off plus how dry that soil looks tells me the tree is not getting enough water.
Its losing leaves because its too dry and cant maintain them and is dropping them to reduce transpiration (water loss) through the leaves because its not getting enough water.
The fact that you are seeing it losing leaves the day after you water it is IMO not because you watered it, but because its been too damn dry and has already decided to sacrifice the leaves.
If you dont want to believe me, its your tree and your choice.
