Inconsistent Distance Between Top System and Page Margins in Parts

In a score I have been working, I have noticed that there is in an inconsistent margin between the top system of music and the page margin. This inconsistency applies across all of the parts, and the difference between the right and left pages is the same. Maybe this is caused by the plugin Export Layout Breaks to Parts, which I used for the first time on this score. I have never had this issue happen- is there any way to fix it? Is it an issue in Format>Style that I'm missing? The issue occurs no matter the header type- whether it is the same for each page or different.

Thanks for any help!

(The issue is most noticeable in the Reed 3 part, which I have worked on the most.)