Image Segmenter Function to apply to set of images

After performing segmentation on a wright-giemsa bone marrow aspirate image with Image Segmenter (just the graph cut feature) with good results and then exporting as a function, i tried to use this function to perform on a different image that has similar features (same kind of cells, same staining, just a different field). It did NOT work at all. How does one apply a function on what is done on a representative image to a set of similar images?

what is the 'right' way of doing graph cut?

how long is the foreground line supposed to be if I am to identify the nucleus? should I draw on the entire nucleus with a long line or a circle?

should I randomly draw on the background or should I draw a circle just outside and around the foreground (nucleus)?

should I do this drawing of the foreground and background extensively, or just 4-5 times on those that are the most representative?