McPan and size of image...

I'm getting problems with the size of image. I use McPan on about only a upper left quarter of the project .
about 400x400 for slider size and 1024x650 document size.
_root.nMC.slideToPoint(id_bt._x-200,id_bt._y-200) for adjusting the map when clicking on a menu
820x820 for the map

It appears that I can't put a map greater than 800x800, otherwise the sliding factor is unmatching and the map slides completely out of the slider; the sliding movement seems to be proportionnal with the size of the image. How can I interact with the deplacement scale? What is the relationship between all these elements? how can I use bigger image (let's say 1200x1200)?

2nd question (sorry if I abuse) :
I want the start and stopmotion to be progressive (ease-in and ease-out). Is this possible?

Thanks for your response
... and big thanks again for this great tool.