I just tried printing out a 2 page target for use with an iSis and the positioning is definitely off to the left side. The target size is specified as 7.8 x 7.24 inch which has been printing fine up to now on 8.5 x 11 in portrait mode. To give you an idea of how far off it is, the upper left is supposed to have an A1 and only has 1 printed and the lower left is supposed to have A19 and only has 19 printed. The diamonds on the left are 1/8" from the edge of the paper. The 7900 frequently prints a hair to the left but has never been this far off.
Using latest Epson drivers and OS 10.6.5.