Think practically. Tyrion's a particularly feisty dwarf in the first season, and that's pretty much all he's known for. Wine, woman, and a waddling walk. So when one of your three specialties is too tall, it's a problem. Thankfully he found Shae within reach (because that turned out so well...) but the practicalities wouldn't have been far from his mind throughout his time with her. Still, the loose ladies of Westeros are only interested in the size of the bag of money he'd take with him to brothels across the continent, and being a Lannister, having the coin wasn't exactly an issue.