AH-HA! Why didn't you say so in the first place?
When you ask about the meaning of a card without letting us know the situation, then we end up throwing everything at you that it could mean, rather than narrowing it down to more likely things. HPS, for example, is all about secrets, but that isn't ALL she is about. The one thing you missed in your upright view is that she is isolated and usually viewed as a maiden or nun.
Now, once again, we don't want to go to the extreme opposite of that, because the Tarot would have likely just given you, oh, the Queen/Wands if the suggestion is to be very extroverted and sizzling hot in bed rather than remote and mysterious.
But HPS rx can certainly advise that your person ease up on being remote, mysterious and too secretive about sexual wants and needs. Being mysterious and secretive is great for flirting. But once in bed, it can work against a person. The partner wants to know what their lover likes and how to make them happy--if that lover won't say, that can frustrate the partner. He/she may wonder if they're bad in bed; may not get as excited or into it if they're not getting any sounds or responses, or any good feedback. He/she may wonder why they're not being praised or hugged or at least told "I don't like that, can you do it different?"
So, I think the advice is relatively simple. To bring balance to this sexual relationship, some secrets must be revealed, however dark, strange or painful (and I'd certainly view an HPS rx as having dark/painful secrets). When it comes to sex, we often have secrets we don't want to share. Maybe we fear we'll be judged for some kink that turns us on. Maybe it's difficult to explain something bad that happened to us and makes enjoying the sex hard. Maybe we just don't want to offend our partner by admitting they're not good at what they're doing and practice is needed. Or maybe we desperately want to hold on to our "mystery." It may seem wise not to tell our secrets, but in this case, it's better to be 'un-wise" and reveal ourselves.