I have found that sometimes you type in a dimension and Access alters it a bit, even if it's a dimension that you copied from some other control on the same report/form. I never figured out why but didn't really try. That's because invariably there's always a bit of white space between the last character in a value and the end of a control and typically, you don't put borders around most report controls anyway so who's to know it's not exactly what I typed in for a width value?
I suppose you could try copying from one report to another and see if the desired value holds. I'd say it could be an issue with gridline spacing in the design grid except that you can't have one setting for one report and a different setting for some other report. Perhaps it has something to do with horizontal placement on the grid, then when you try to size it, it wants to adjust the width to conform to the grid. Perhaps check the placement of the left/top position (you didn't say if it was horizontal or vertical dimension you were struggling with) and see if they're the same in both reports. What I don't get is why you'd create 2 reports that are basically the same if the query is based on the same table.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.