It's a combination of strengths that makes it overwhelm any male. We had hints of this previously when Asmodean claimed that thirteen of the weakest women could shield most men, implying that some men would be able to resist them. He went on further to say that thirteen weak Aes Sedai (stronger), would shield any man without exertion.

In TGS Rand approaches the damane with the Choedan Kal and he says that by drawing only a little through it, he could probably match a full circle. That is strong evidence that a man with a sa'angreal or angreal who exceeds natural maximum male strength can fight larger circles without being shielded.

It also disproves the 'magic number' theory which states that even if Rand held the Choedan Kal and drew all of saidin into him, a circle of thirteen could overwhelm him with ease.

I also consider this to be the reason why Jaric Mandoran destroyed the whole of Tzora during the Breaking without being stopped. The fact that he destroyed the city with a single giant flame implies that he was using a sa'angreal, and therefore could not be stopped. But that's a small side theory