I've had a quick search of the archives and can only find references to measuring big and people being sent for a scan, not the actual pattern that measurements follow.
I'm measuring 2 weeks over but have been all the way through (am 34 weeks). My midwife says the baby feels average, it's just that I have quite a lot of fluid. She doesn't sound worried in the slightest but does smile at every appointment and say 'lots of fluid'. The baby isn't in an unstable lie (ceph since 26 weeks) and the fundal height is consistently 2cm ahead.
I just wondered, if there is too much fluid, so much so that it was polyhydramnios, would your fundal discrepancy increase over time instead of remaining consistent?
I suppose it's only on my mind because with dc1 I had a PROM and I know that if you have excess fluid and this happens, you need to act quickly.