I think a more accurate version of what Astarte was trying to say would be 'Titania, let your Fairies and Pixies grow into your body size, then your games will become much better'. That is, having them go from their petite, miniature sizes to a more normal human size.
On an entirely different note, I like the way Titania was handled here -- there's a lot of fun to be had with the ideas, especially with the idea of a majestic fairy queen being super-happy you're doting on her.
Like you said before i mean that the fairies and pixies should have the same body size as her queen that makes the funny and lewd games more interesting for both sides. On the other side titania can shrink humans to fairy body size but unclear if that is possilbe with her powers. It's a strange point that no profile say that monstergirls can change their body size because this is normaly a easy way with magic.