Cura 2.4 reports that the (printer-dependant) G-Code mode prevents the "Flow" (extrusion rate adjustment percentage) setting from being available. Why? I am using an Ultimaker 2+. Is a firmware update required?
I know the "Flow" can by dynamically adjusted on the 3D printer (either in materials or while printing).
I am asking because I have small holes (1 mm) that seem to slice fine but get filled so the extrusion probably is not that optimally tuned. I suspected reducing the material rate would improve this but changing it on the printer (97%) did not yield noticable results and below that it looked worse.
For the Ultimaker 2 flow is typically handled on the printer.
You could make a feature request at github to let Flow be enabled for Ultimaker 2 printers.
As for your problem: that sounds more like a dimensional accuracy problem to me. I suggest setting Horizontal Expansion to -0.15mm.