So it can be a small beam, such as the one shot by Moiraine, or a large mass, such as the one Rand used on the Burrow. We've seen it in various forms before - when Rand directed a stream between Asmodean and Lanfear, it was a massive blast, and when he used it in other occasions, it was a more focused laser beam.

When Rand balefired the Barrow, it actually took him longer to set it up then it did in the past, because it seems that he created a massive concentration of the reality-destroying effect, and then laid it down over the entire Palace.

Also, it seems that your intent determines the effect - if you aim at an individual person with a small amount of Power, a small laser-like blast hits that individual (Semirhage and Elza were taken in this way, clothes and all), but if you created the beam and then spread it around, trying to blast someone but not necessarily aiming for them precisely anything that gets in the way save for cuendillar, gets destroyed - this would account for the 'carving' phenomena we are told happens in some instances; the Black Ajah Sister with the balefire-ter'angreal who detected Nynaeve and Moghediens' fight, for example, was struggling to control the beam so much that she wasn't aiming at anyone, and was just activating the object, and pointing it in a general direction.