If I remember correctly the 2MB of the Picasso II is mapped inside the Zorro II address space, so you'll have 2MB of the 8MB used leaving 6MB.
My Picasso II+ has the option to run in segmented mode or something which apparently doesn't map the 2MB into the Zorro II address space.
It's very slow when jumpered like that though, not sure if the Picasso II has it too.
