I think the % chance is supposed to be this. First you assume that the other person has AIDS and you do not. Then you (sexual activity of whatever sort). The 1 in 220 is supposedly the chance that after (sexual actiivty), you now have AIDS.

AIDS is actually kind of hard to transmit from a single sex act, even if you're 100% sure the other person has it, is what I understand.

But the 1 in 220 can't be "transmittal via vaginal hetero sex" in general, it has to be either male-to-female or female-to-male. From some stuff I read more than a decade ago, I'm pretty sure that the 1 in 220 is male-to-female, with female-to-male being a much lower chance of infection. But I could be wrong about that.