For all 6 fields, check the box that says "Also resize enclosing part". That will close up the extra height of the trailing grand summary part. (Note that this checkbox has never worked for any of the header parts or any of the footer parts -- it is a decades-old bug in FileMaker that they have never fixed.)
If your fields themselves are not sliding upwards, make sure that each row of fields (going down vertically) are perfectly aligned on their very leftmost margins and very rightmost margins. Then, on each row of fields (going across horizontally), make sure that each row's fields are perfectly aligned on their topmost margins and bottommost margins.
Excellent! Checking the 'also resize enclosing part' did the trick
I forgot to mention -
I guess I should be glad I'm only using this in 'grand summary' part. The problem with other parts has been noted should I need to do this in another report. Thanks for including that piece of information