A very popular question that is always met and commented on in the same fashion. Tall men and short ladies know what they're getting into when they court each other. Men, like women arent seeking a body double, but a person they are attracted to - often looking quite different then them. Yes, big height differentials make for less classic love-making photo-ops, but who's to say Lamar Odom and Khloe aren't doing just fine (at least when it comes to grinding).
The major issue with a 12 inch differential, when grinding or inter-coursing, is kissing can be more challenging. This requires a level of emotional comfort and flexibility between you two. Often kissing in a new relationship (though intimate) is a way of burying yourself, offering some covering from the naked eye-to-eye truth of being entered or inserted into a new person. Without the kiss you are left to your own eyeballs and minds. That's OK. Take it as a good thing. It forces you to say, am I comfortable in general with this tall dude? And he, "Am I comfortable with this shorty grinding me?"
Of course if the man is on top he has more range and can bend about making kissing and grinding a two-part affair. That is, unless his wang is terribly small or he has multiple back herniations.