In a sense, yes. The whole gimmick of the Virgin City is that you can't see it, or interact with it if you're not a virgin. If you could still feel your way in, I'd think that the Evil Sorceress would have noticed there was a secret city right at her doorstep this whole time. So, effectively, if you're not a virgin, it's as if the city was on a whole other plane of existence.
With that in mind, it's not a huge stretch of the imagination to assume that, should someone have sex within the city, they effectively fade out of it, as they can no longer see or interact with it. So, the way the potion works is that it tricks your brain into believing that you're no longer a virgin, thus for a period of time, you can't get back in. It is possible to see through the trickery of the potion, however, hence why there were a couple of times where Ivan was fading away again. They were still technically within the city, and his brain was starting to say "Nope, still a virgin".