Soul,
What you are experiencing sounds quite normal. It is accurate that at 20 weeks the fundus (top of your uterus) roughly = your umbilicus or belly button. However you are an old hand at the pregnancy game and many women who have had mulitiple pregnancies experience what you are. Women who have had a few pregnancies often measure a little more than dates when the fundus is measured too. I have! Remember that the uterus isn't static, yor baby is moving lots and if it is lying up high or to the side and gives you a nice prod then it is more than probable that this would be felt higher than your umbi.

I think you can expect only good news on Monday. Your baby is moving well by the sounds and the movements are strong. I look forward to hearing wonderful things from your visit.