Movement rates over different terrain

[The Bruce]

I have searched for an answer to this but can't find one.

Does anyone know if campaign map movement rates over different ground_types can be modded. For example, swamps reduce movement but can this effect be increased? Or is it all hardcoded?

[Gigantus]

Movement rates over different ground_types appear to be hard coded. You can change the individual movement rates of unit classes but not over different terrain like on the battle map.
How else to explain the greatly reduced movement rate of ocean going ships when you sail to America?

[The Bruce]

How else to explain the greatly reduced movement rate of ocean going ships when you sail to America?

Well you could explain it by a secret modifier in a file I had overlooked

I had expected it was indeed hardcoded. Bloody shame though!