Thanks for your post. Yes, this is an issue with the GE for small sub-areas/reaches.
As you have identified, the work-around is to edit the reach length and sub-area area data directly into the catchment file using a text editor. When you do this, you will need to adjust the data being used in the actual RORB control codes which start below the GE data.
Having done this, it is best not to edit the file again in the GE or you will overwrite your changes.
We’ll add this onto the bug/enhancements list and try to get it fixed in the next release. It would be helpful if you and other users could provide some feedback on the size of the smallest sub-areas you have worked with to ensure that we can capture these.