Your users are inputing their reports how? w/ filemaker or IWP or CWP or email?
On the report, if you specify the comment field, it will include white space or cut the text.
What are your tables and how is the printout layout formatted?
The quick fix:
Select the field in layout mode and choose Set Sliding/Printing in the Format menu.
Set your field to slide up, also shrink size of enclosing part.
Give these same settings to every layout object in the same layout part that is even with or below this field.
Resize your field so that it is large enough to display the largest possible list of comments as it will shrink but won't "grow".
The sliding will not be visible in Browse Mode, but will be visible in preview, when you print, when you save as PDF.
A better fix option:
Take your comments and store them in a related table where each comment occupies one record. You can enter these comments on a layout that uses a portal.
Create a summary report based on your new comments table and add the other fields to a sub summary part. The resulting report will work with any number of comments as long as each individual comment record has a field large enough to display that one entire comment.
Here's a link to a simple tutorial on setting up summary reports that you may find useful:
Creating Filemaker Pro summary reports--Tutorial