Is it normal i imagine a 3-some to orgasm best during sex with wife?

I've found my best orgasm comes when I imagine I'm making love to both my wife, and her sister at the same time. They look basically identical, despite her sis being about 8 years older. While my wife is more submissive and shy / doesn't know she's a bombshell, her sister Knows she's hot and flaunts it.

My wife has her best orgasm with me as well while I'm imagining this scenario, unbeknownst to her.