I've run disk set 18 through Michael's Pipeline with apertures 3, 4 & 5. With the current focus discussion I thought some of these plots may be relevant. Hopefully they're self explanatory. Sorry its so brief, I'm intending to write up a tech note shortly.
I combined a whole disks worth of data (ie the .coo output file) for each graph. Although most of the disks plots are similar they do vary a bit. 18i is reasonably representative.
Disk 18i fwhm, roundness and sharpness by CCD Column
Disk 18i fwhm, roundness and sharpness by CCD Row
Disk Set 18 fwhm plots by CCD Column