You don't want to add your aftershave to melted soap that is hot. The heat will make the alcohol and fragrance evaporate faster, making it smell stronger then, but leaving less scent for when it cools.I've noticed that the hotter it is, the stronger the scent. Once it cools down, the scent should smell "weaker."
You want to allow your soap to cool to just before it starts to solidify before to add the aftershave, to preserve the scent.