Wait!

I just realised. RJ says that in the AoL, entire cities were balefired, and hundreds of thousands were killed in one go.

That must mean that there is a way to create a balefire stream wide enough to encompass an entire city with a single blast.

We know that this city destruction happened before the creation of the Choedan Kal. We also know that CK offered more power than anything available to them yet. So it is possible, with less power than CK, to create a wider balefire bar. That must mean that it IS possible to regulate the width&height of the balefire separately from the power, and that Rand who did not want to destroy the world yet, and who had almost full access to LTT at this point could and probably would have created balefire that while wide, was not all that strong in order to minimise the damage.