I have added a custom field as Remarks after Description in Sales Invoice → Line Item and selected it to be displayed in Printed Documents. When I use that column and type in values the column width is very large and not proportionate to the size of text in it. This is even more increased when I use the PDF option to create a PDF file.
Sorry I have forgotten to mention that I have tried the Plain and the Smooth Gray themes both without any changes to the theme. Also I have tried the same with Tax and without Tax included.