From World Guide I In the Chapter: Monsters that Imprison
"In the case that the partner was a monster that has a grotesque lower body, such as snake, spider, etc. even if the man at first hated and feared that grotesque body, once he has sex with her, even that grotesque body will appear beautifully lewd, and he'll end up feeling that it's unbearably sweet."
So yeah the aggresive ones will feel provoked to show you how good they are, while the more reserved ones will charm you to give it a try