You dont provide enough information to help. Need to see examples or screen shots of your setup of the imposition node and workflow. The forum wont let you attach .jpg so you might take a some screen shots or export your workflow using FreeFlow Core Exchange and then zip these files and attach to post. If we can see these things we can provide a quick answer and fix. Also a sample of the input file would be good as well so we can see start to finish.
We are having an issue using a 12x18 Freeflow Core workflow. When it is sent to the Iridese Workfront server and printed its coming out as a 11x17 im and cropped. Anyone ever have this issue? We are also having this issue with a 13x19 workflow.