as title.... I've upgraded to Sailfish

Managed to get GPX running with Slic3r, thats fine.

but my prints are not starting in the middle of the bed,
instead they start to the top right (as I look at the bed).

Saved the home coordinates before I did and loaded same into Sailfish.
x = 152mm
y = 75mm

Set Bed shape to :
x = 228 x and y= 150


what needs to be done to make the prints start in the middle?

Thanks
Ray