You have run into the problem of minimum page size.
With OSx you can set the custom page size outside the minimum and maximum page sizes supported by the printer, all without any warning. If the page size is set below the minimum then an aproximate A4 size normally from the centre of the image is printed, if the page size is set above the maximum then normally a coloured stripe patern is printed.
The minimum page length for the 9600 are 7.17 inches or 18.20 cm.
Not 100% sure of the maximum length but it is about 94 inches.
As to cutting off 2 inches aty the begining of the print, this will be because you are printing borderless with single or double cut selected in the roll paper options.
The three options are normal (where you will get a margin dependent on the roll paper margins set in the printer set up menu), single cut (on the first print a 2 inch section of paper is cut off with about 1.5mm of the print, at the end of the print (if another job is queued) the printer will then cut when part of the second job has printed ant the junction of the prints is under the cutter). Double cut (a 2 inch section of paper is cut off with about 1.5mm of the print, at the end of the print The paper is advanced and the print is cut leaving about 1.5mm of the print on the roll, this is then cut off in the 2 inch piece at the start of the next print).
sorry for the long winded explanation.