When the Romans came

We know our coast line over the centuries has changed a lot. Eroded in some places – e.g., locally the loss of the village of Pende to the sea – but built up in others as evidenced by the spit created for Shoreham beach. Generally though it seems for the majority of the south since Roman times the coast has been eroded but by how much?
I’m sure erosion doesn’t happen at a constant rate but there is a indication in our 1724 Phillimore Margary map that has the attached notation entered just below Hove. It suggests that six perches were lost in 25 years. I’ve forgotten, perhaps never knew, the old surveying measurements so had to look up perches but anyway six of them apparently equate to 33 yards (still can’t be bothered with metric measurements) and with 1,760 yards to a mile (funny how some numbers stick in your mind and that one has) the loss at a constant rate would take 1,333 years to lose a mile.
I’ve never been good at sums and bet I’m wrong again but if for once I’m not then it seems when the Romans came our coast may have been a mile or two further out.