In the Aspen.ini file at %appdata%/xitron/plugsins/aspen.ini/ you need to add a new preference "DeviceWidthPixels", which allows you to set the device width.
This ini file is read by the plugin during startup and used to configure the device.
In the absence of any entry in the aspen.ini file the aspen plugin will default to 8.64" or 13824 pixels. If you desire to change to 8.72" you must set this value to 13952 pixels.
Explanation of the pixel to inch conversion: (inches * pixels per inch resolution) = device width in pixels. e.g. (8.72*1600)=13952
If you start with the larger of the two requested values (13952) and reduce the value to (13824) between RIP sessions this seems to work properly but if you go the other way the smaller value remains valid. In other words, a RIP set up for 8.64" will not easily move to 8.72", but moving from 8.72" to 8.64" does work easily.
What does "easily" mean in this case?
To switch from 8.64 to 8.72 you must delete the Aspen device and the associated Page Setups in the RIP, shut the RIP down, make the change and restart the RIP. Then you must recreate the Aspen device (device manager) and the Page Setups (page setup manager).
For this reason it is expected that only a knowledgable technical person will attempt this in the field.
The entry in the INI file looks like this: