But, it's entirely possible the only reason your fig is doing so well in terms of growth and fruit is BECAUSE it's able to spread wider in the soil via that root that's gone through the bottom... so if you restrict it in a pot, you may not get such good results next year.

OK point taken Bamboo! Thx. I was always told that by restricting the roots you got better fruit, however this is the first year that the plant has done so well, and the first year that I've not been able to move it...........humph!
So you must be right Bamboo!

I know that some people plant them in the ground, having first made, usually out of brick, a sort of hemmed in area in the soil at the base of the plant, though not solid at the bottom, usually 3 or 4 bricks deep, in a square or 3 sides against the wall behind, roughly a foot to 18 inches wide. This is said to increase flowering - I guess it gives a similar effect to the situation you've got now, where the top part of the roots are restricted, but access to soil is available at the bottom.

Whether any of this really makes a difference I don't know - I certainly know of someone in Devon who has never restricted the roots on his Brown Turkey fig, and yes, the plant gets large in a summer, but its always covered in fruit, though he prunes it hard in winter. Its also said that Agapanthus do better with restricted roots - I can't say I've found that at all true either with the hardy ones, they flower much better in open ground.

I totally agree about Agapanthus, Bamboo - they flower much better in open ground. Tried them in a pot and not one flower despite growing well and looking healthy for three years - transferred to open ground last year - covered in beautiful white and blue flower spikes

Yep, that's been my experience, for sure...